Help: Revise the cmake(1) manual

Extend the Synposis, and provide links to manual sections. For consistency, add new sections for cmake --open and cmake --help-* modes.

Separate the Introduction from the description of the Makefile Generation Mode, and provide entry-level explanations on how to use cmake.

Print the name of the cmake executable in boldface, so that it does not appear less prominent than other shell commands (which are underlaid with links). Similarly for cpack and ctest in their manuals.