Add multi-lingual inflectors and pluralize/singularize methods

[hipsterjazzbo]

There are several issues that have been opened about these methods, and then closed with the concern that they wouldn't be able to be multi-lingual.

I hope this approach will work. It is multi-lingual, new languages are easy to add (as long as one speaks the language and a bit of regex), and could be added on a project basis without needing to register anything with Stringy.

I have set up, to start, Inflectors for English, Spanish, French, Norwegian Bokmal, Portuguese and Turkish.

This still needs tests, but I just wanted to have a discussion first before I do those :)

For the record, I'd also be happy to update documentation before merging, both in terms of the methods and how to write/add a new inflector.