DOC: Move the ITK_DISALLOW_COPY_AND_ASSIGN to public section.

Following the discussion in
https://discourse.itk.org/t/noncopyable/648

and the patch sets:
http://review.source.kitware.com/#/c/23289/
http://review.source.kitware.com/#/c/23294/

move the `ITK_DISALLOW_COPY_AND_ASSIGN` macro to the public section of a
class in the `Coding Style Guide` chapter.

Also, add an explanation about it in the `Using Standard Macros`
section.

Author: Jon Haitz Legarreta

SoftwareGuide/Latex/Appendices/CodingStyleGuide.tex

@@ -2616,6 +2616,8 @@ \subsection{Empty Lines}
   public ImageToImageFilter< TInputImage, TOutputImage >
 {
 public:
+  ITK_DISALLOW_COPY_AND_ASSIGN(BoxImageFilter);
+
   /** Standard class type alias. */
   using Self = BoxImageFilter;
   using Superclass = ImageToImageFilter< TInputImage, TOutputImage >;
@@ -2632,8 +2634,6 @@ \subsection{Empty Lines}
   void PrintSelf(std::ostream & os, Indent indent) const override;
 
 private:
-  ITK_DISALLOW_COPY_AND_ASSIGN(BoxImageFilter);
-
   RadiusType m_Radius;
 };
 
@@ -3038,6 +3038,8 @@ \section{Using Standard Macros}
 \item Object modified time is properly managed.
 \item Debug information is printed.
 \item Reference counting is handled properly.
+\item Disallow copy semantics by deleting copy constructor and assignment
+operator.
 \end{itemize}
 
 Some of the more important object macros are:
@@ -3048,6 +3050,9 @@ \section{Using Standard Macros}
 \item \code{itkTypeMacro(thisClass, superclass)}: Adds standard methods a
 class, mainly type information. Adds the \code{GetNameOfClass()} method to the
 class.
+\item \code{ITK\_DISALLOW\_COPY\_AND\_ASSIGN(TypeName)}: Disallow copying by
+declaring copy constructor and assignment operator deleted. This must be
+declared in the \textbf{public} section.
 \item \code{itkDebugMacro(x)}: If debug is set on a subclass of
 \doxygen{Object}, prints debug information to the appropriate output
 stream.