Help: Organize and revise the cmake-generators.7 manual

Move "extra" generators to their own section instead of duplicating them
for each corresponding main generator.  Divide the list of main
generators into command-line and IDE sections and sort the names within
each section.  Document the environment from which each kind of
generator may be used.

Add a section to each "extra" generator documenting which main
generators may be used with it.
Merge topic 'doc-generators-cleanup'

beec9db Help: Organize and revise the cmake-generators.7 manual