CMake builtin documentation handling

CMake,CPack,CTest builtin documentation

All CMake tools command line do have some builtin documentation support. The tools (cmake, cpack, ctest) supports a variable subset of:

 ctool --help-command[-list] 
 ctool --help-module[-list]
 ctool --help-variable[-list]
 ctool --help-policy[-list]
 ctool --help-property[-list]
 ctool --help-full
 ctool --help-html

for the detail see:

 cmake --help
 cpack --help
 ctest --help

This builtin documentation comes from 2 different places:

1. static variables in C++ sources
2. text surrounded by markup in CMake script files

Documentation in C++ sources

This is the primary source of builtin documentation.

Documentation markup in CMake script files

This source is available since CMake 2.8.8 and is currently only used by CPack.