Add acronym support

[hut8]

Hey there. Thanks for this awesome library.

The Rails inflector supports user-defined acronyms, so that http_client could be transformed into HTTPClient (for example). See https://github.com/rails/rails/blob/f2489f493b794ee83a86e746b6240031acb8994e/activesupport/lib/active_support/inflector/inflections.rb#L78 for details.

I may have time in the near future to implement this. Would you accept a PR if I did?

[nbubna]

Oooh, that is a fascinating idea. Of course, i can guarantee i'd take the PR without seeing it, but i'm definitely open to it. It's a case situation i've run into myself.