add pluralize & singularize

[tippenein]

~Feature Request~ I need something like this: https://github.com/rails/rails/blob/master/activesupport/lib/active_support/inflections.rb

It would seem appropriate to put this functionality along with your work.

[tippenein]

Initial tested "irregular" countables here

I'm not sure the best way to generate this mapping is though. You might not want to add a regex dependency and generating the singular/plural versions of these into a Bimap is not plausible.

[tippenein]

41 implements this

[elcuy]

Closing this since it's solved