DOC: Add documentation about command-line CMake and Remote Modules.

Add documentation to
- Show how to use CMake command-line tool.
- Show how to use ITK as an external library.
- How to contribute with a remote module.

In the latter case, many ITK wiki contents were re-used:
https://itk.org/Wiki/ITK/Policy_and_Procedures_for_Adding_Remote_Modules

Addresses:
https://insightsoftwareconsortium.atlassian.net/projects/ITK/issues/ITK-3211?filter=myopenissues

Author: Jon Haitz Legarreta

SoftwareGuide/Latex/DevelopmentGuidelines/CreateAModule.tex

@@ -8,6 +8,9 @@ \chapter{How To Create A Module}
 dependencies on other modules, which it declares. A module is defined with
 CMake scripts that inform the build system of its contents and dependencies.
 
+The modularization effort significantly improves the extensibility of the
+toolkit and lowers the barrier to contribution.
+
 Modules are organized into:
 
 \begin{itemize}
@@ -969,3 +972,105 @@ \subsection{CMakeList.txt}
 set(ITKVideoBridgeOpenCV_SYSTEM_INCLUDE_DIRS ${OpenCV_INCLUDE_DIRS})
 set(ITKVideoBridgeOpenCV_SYSTEM_LIBRARY_DIRS ${OpenCV_LIB_DIR})
 \end{minted}
+
+\section{Contributing with a Remote Module}
+\label{sec:ContributingRemoteModules}
+
+For most ITK community members, the modularization of the toolkit is relatively
+transparent. The default configuration includes all the (default) modules into
+the ITK library, which is used to build their own ITK applications.
+
+For ITK developers and code contributors, the modular structure imposes rules
+for organizing the source code, building the library and contributing to the
+ITK source code repository.
+
+A Module may be developed outside the main ITK repository, but it may be
+made available in the ITK repository as a Remote Module. The Remote Module
+infrastructure enables fast dissemination of research code through ITK without
+increasing the size of the main repository. The Insight Journal
+(\url{http://www.insight-journal.org/}) adds support for ITK module submissions
+with automatic dashboard testing (see Section~\ref{sec:CDash} on
+page~\pageref{sec:CDash} for further details).
+
+The source code of a Remote Module can be downloaded by CMake (with a CMake
+variable switch) at ITK CMake configuration time, making it a convenient way to
+distribute modular source code.
+
+\subsection{Policy for Adding and Removing Remote Modules}
+\label{subsec:RemoteModuleAddRemovePolicy}
+
+A module can be added to the list of remotes if it satisfies the following
+criteria:
+\begin{itemize}
+\item There is a peer-reviewed article in an online, open access journal (such
+as the Insight Journal) describing the theory behind and usage of the module.
+\item There is a nightly build against ITK master on the CDash dashboard that
+builds and passes tests successfully.
+\item A name and contact email exists for the dashboard build. The maintainer
+of the dashboard build does not necessarily need to be the original author of
+the Insight Journal article.
+\item The license should be compatible with the rest of the toolkit. That is
+it should be an Open Source Initiative-approved
+license\footnote{\url{https://opensource.org/licenses}} without copyleft or
+non-commercial restrictions. Ideally, it should be an Apache 2.0 license
+assigned to the Insight Software Consortium as found in the rest of the
+toolkit. Note that the module should contain neither patented code, nor
+algorithms, nor methods.
+\end{itemize}
+
+At the beginning of the release candidate phase of a release, maintainers of
+failing module dashboard builds will be contacted. If a module's dashboard
+submission is still failing at the last release candidate tagging, it will be
+removed before the final release.
+
+Module names must be \textbf{unique}.
+
+At no time in the future should a module in the main repository depend on a
+Remote Module.
+
+\subsection{Procedure for Adding a Remote Module}
+\label{subsec:ProcedureAddingRemoteModules}
+
+The repository
+\begin{center}
+  \url{https://github.com/InsightSoftwareConsortium/ITKModuleTemplate}
+\end{center}
+
+provides a useful template to be used as a starting point for a new ITK module.
+
+The procedure to publish a new module in ITK is summarized as follows:
+\begin{enumerate}
+\item Publish an open access article describing the module in an online, open
+access journal like The Insight Journal.
+\item Submit a Gerrit patch (see Section~\ref{sec:GitRepository} on
+page~\pageref{sec:GitRepository) that adds a file named
+\code{Modules/Remote/<module name>.remote.cmake}. This file must have the
+following:
+\begin{enumerate}
+\item Dashboard maintainer name and email in the comments.
+\item A call to the \code{itk_fetch_module} CMake function (documented in
+\code{CMake/ITKModuleRemote.cmake}) whose arguments are:
+\begin{enumerate}
+\item The name of the remote module. Note that in each
+\code{<remote module name>.remote.cmake}, the first argument of the function
+\code{itk_fetch_module()} is the name of the remote module, and it has to be
+consistent with the module name defined in the corresponding
+\code{<remote module name>.remote.cmake}. To better distinguish the remote
+modules from the internal ITK modules, the names of the remote modules should
+\textbf{NOT} contain the ``ITK'' string prefix.
+\item A short description of the module with the handle to the open access
+article.
+\item URLs describing the location and version of the code to download. The
+version should be a specific hash.
+\end{enumerate}
+\end{enumerate}
+\end{enumerate}
+
+After the Remote Module has experienced sufficient testing, and community
+members express broad interests in the contribution, the submitter can then move
+the contribution into the ITK repository via Gerrit code review.
+
+It is possible but not recommended to directly submit a module to Gerrit for
+review without submitting to Insight Journal first. There are no established
+rules on whether a module should be directly merged into the main repository or
+not.

SoftwareGuide/Latex/Introduction/Installation.tex

@@ -441,6 +441,69 @@ \subsection{Advanced Module Configuration}
 displayed (Figure \ref{fig:ConfigITKDefault}); these messages are sorted in
 alphabetical order by module names.
 
+Those who prefer to build ITK using the command line are referred to the online
+cmake command-line tool
+documentation\footnote{\url{https://cmake.org/cmake/help/latest/manual/cmake.1.html}}.
+Only some typical use cases are shown here for reference.
+
+\begin{itemize}
+\item \textbf{Example 1}: Build all default modules.
+\small
+\begin{minted}[baselinestretch=1,fontsize=\footnotesize,linenos=false,bgcolor=ltgray]{bash}
+cmake [-DITK_BUILD_DEFAULT_MODULES:BOOL=ON]
+      ../ITK-build
+\end{minted}
+\normalsize
+
+As \code{ITK\_BUILD\_DEFAULT\_MODULES} is \code{ON} by default, the above can
+also be accomplished by
+\begin{minted}[baselinestretch=1,fontsize=\footnotesize,linenos=false,bgcolor=ltgray]{bash}
+cmake ../ITK-build
+\end{minted}
+
+\item \textbf{Example 2}: Enable specific group(s) of modules.
+\small
+\begin{minted}[baselinestretch=1,fontsize=\footnotesize,linenos=false,bgcolor=ltgray]{bash}
+cmake -DITK_BUILD_DEFAULT_MODULES:BOOL=OFF
+      -DBUILD_EXAMPLES:BOOL=OFF
+      -DITKGroup_{Group1}:BOOL=ON
+      [-DITKGroup_{Group2}:BOOL=ON]
+      ../ITK-build
+\end{minted}
+\normalsize
+
+where \code{ITKGroup\_{GroupN}} could be, for example,
+\code{ITKGroup\_Filtering} or \code{ITKGroup\_Registration} for the
+\code{Filtering} and \code{Registration} groups, respectively.
+
+\item \textbf{Example 3}: Enable specific modules.
+\small
+\begin{minted}[baselinestretch=1,fontsize=\footnotesize,linenos=false,bgcolor=ltgray]{bash}
+cmake -DITK_BUILD_DEFAULT_MODULES:BOOL=OFF
+      -DBUILD_EXAMPLES:BOOL=OFF
+      -DModule_{Module1}:BOOL=ON
+      [-DModule_{Module2}:BOOL=ON]
+      ../ITK-build
+\end{minted}
+\normalsize
+
+where \code{Module\_{Module1}} could be, for example, \code{Module\_ITKFEM} for
+the non-default, built-in \code{FEM} module, or \code{Module\_Cuberille} for
+the \code{Cuberille} remote module.
+
+\item \textbf{Example 4}: Enable examples.
+\small
+\begin{minted}[baselinestretch=1,fontsize=\footnotesize,linenos=false,bgcolor=ltgray]{bash}
+cmake -DITK_BUILD_DEFAULT_MODULES:BOOL=ON
+      -DBUILD_EXAMPLES:BOOL=ON
+      ../ITK-build
+\end{minted}
+\normalsize
+
+Note that \code{BUILD\_EXAMPLES} is \code{OFF} by default, and
+\code{BUILD\_EXAMPLES=ON} requires \code{ITK\_BUILD\_DEFAULT\_MODULES=ON}.
+
+\end{itemize}
 
 \subsection{Static and Shared Libraries}
 \label{sec:StaticSharedLibraries}
@@ -592,6 +655,72 @@ \section{Getting Started With ITK}
 to see the output. It is therefore preferable to run the executable from the DOS
 command line by starting the \code{cmd.exe} shell first.
 
+\section{Using ITK as an External Library}
+\label{sec:UsingITKAsExternalLibrary}
+
+For a project that uses ITK as an external library, it is recommended to
+specify the individual ITK modules in the \code{COMPONENTS} argument in the
+\code{find_package} CMake command:
+
+\small
+\begin{minted}[baselinestretch=1,fontsize=\footnotesize,linenos=false,bgcolor=ltgray]{bash}
+find_package(ITK REQUIRED COMPONENTS Module1 Module2)
+include(\${ITK_USE_FILE})
+\end{minted}
+\normalsize
+
+e.g.
+
+\small
+\begin{minted}[baselinestretch=1,fontsize=\footnotesize,linenos=false,bgcolor=ltgray]{bash}
+find_package(ITK REQUIRED
+  COMPONENTS
+    MorphologicalContourInterpolation
+    ITKSmoothing
+    ITKIOImageBase
+    ITKIONRRD
+    )
+include(\${ITK_USE_FILE})
+\end{minted}
+\normalsize
+
+If you would like to use the CMake ExternalProject
+Module\footnote{url{https://cmake.org/cmake/help/latest/module/ExternalProject.html}}
+to download ITK source code when building your ITK application (a.k.a.
+Superbuild ITK), here is a basic CMake snippet for setting up a Superbuild in
+an ITK application project using CMake:
+
+\small
+\begin{minted}[baselinestretch=1,fontsize=\footnotesize,linenos=false,bgcolor=ltgray]{bash}
+ExternalProject_Add(ITK
+      GIT_REPOSITORY \${git_protocol}://github.com/InsightSoftwareConsortium/ITK.git"
+      GIT_TAG "<tag id>" # specify the commit id or the tag id
+      SOURCE_DIR <ITK source tree path>
+      BINARY_DIR <ITK build tree path>
+      CMAKE_GENERATOR ${gen}
+      CMAKE_ARGS
+          ${ep_common_args}
+          -DBUILD_SHARED_LIBS:BOOL=OFF
+          -DBUILD_EXAMPLES:BOOL=OFF
+          -DBUILD_TESTING:BOOL=OFF
+          -DITK_BUILD_DEFAULT_MODULES:BOOL=ON
+          [-DModule_LevelSetv4Visualization:BOOL=ON]
+        INSTALL_COMMAND ""
+       DEPENDS
+[VTK] [DCMTK]  # if some of the modules requested require extra third party libraries
+ )
+\end{minted}
+\normalsize
+
+More exemplary configurations for superbuild ITK projects can be found in:
+Slicer\footnote{url{https://github.com/Slicer/Slicer},
+BrainsTools\footnote{url{https://github.com/BRAINSia/BRAINSTools}, ITK Wiki
+Examples\footnote{url{https://github.com/InsightSoftwareConsortium/ITKWikiExamples},
+ITK Sphinx
+Examples\footnote{url{https://github.com/InsightSoftwareConsortium/ITKExamples},
+and ITK Software
+Guide\footnote{url{https://github.com/InsightSoftwareConsortium/ITKSoftwareGuide}.
+
 \subsection{Hello World!}
 \label{sec:HelloWorldITK}