register_options for some help-ish and doc-ish tasks.

Testing Done:
https://travis-ci.org/pantsbuild/pants/builds/37842836

Reviewed at https://rbcommons.com/s/twitter/r/1135/
Sync of https://github.com/pantsbuild/pants/commit/abc755a774c12c03c5edcf70d0ad3f11d583be75