Move generated man pages to dedicated directory

Make sure all generated documentation files are stored under
man/generator so they don't clutter up the important files under man.

Additionally it doesn't make much sense to package all files relevant
for the man page creation in the gem so this behavior was adapted too.
Incoporate suggestions
Merge pull request #320 from SUSE/move_generated_man_pages_to_dedicted_directory

Move generated man pages to dedicated directory