Enhance CMake configurations

[gsegon]

This PR enhances installation and packing of the library.

1. The installation installs the mathtoolbox target with:

• {CMAKE_INSTALL_PREFIX}/include/mathtoolbox/*.hpp
• {CMAKE_INSTALL_PREFIX}/lib/libmathtoolbox.a
• {CMAKE_INSTALL_PREFIX}/lib/cmake/MathToolboxConfig.cmake
• {CMAKE_INSTALL_PREFIX}/lib/cmake/MathToolboxConfigVersion.cmake
• {CMAKE_INSTALL_PREFIX}/lib/cmake/MathToolboxTargets.cmake
• {CMAKE_INSTALL_PREFIX}/lib/cmake/MathToolboxTargets-release.cmake (or MathToolboxTargets-debug.cmake for Debug build)

CMake install config is modified such that a dependent cmake project (user project) can find and link mathtoolbox via find_package, for example:

cmake_minimum_required(VERSION 4.0)
project(SomeApp)

set(CMAKE_CXX_STANDARD 20)

find_package(MathToolbox REQUIRED)

add_executable(some_app main.cpp)
target_link_libraries(some_app PUBLIC MathToolbox::mathtoolbox)

target_include_directories(some_app PUBLIC .)

If the library is not found CMake will automatically cache an empty MathToolbox_DIR and the user is expected to provide the path to library install destination cmake directory. Conventionally, this is <install_dir>/lib/cmake.

2. CMake packaging config is setup and enabled. For example, calling

cmake --build build --target package

will package the installation in a number of default formats, namely: MathToolbox-0.3.1-Linux.sh, MathToolbox-0.3.1-Linux.tar.gz, MathToolbox-0.3.1-Linux.tar.Z. See CPack for more options.