Incorporate GeneratePryMan into pry. (continued from 785)

See pull request history https://github.com/pry/pry/pull/785

The failing tests were caused by a date being set in the generated output that was hard set in the fixture.  

Since generate_pry_man.rb writes the html/roff/ronn files to the `man/generate_pry_man/templates/` dir and then moves them to the appropriate folder I adjusted the gitignore to prevent them from being tracked.  

Also wrapped the entire spec file inside a conditional that prevents it from being run in jruby without causing the tests to prematurely exit (per @kyrylo's reccomendation)