Adds ability to specify custom small words and acronyms

[santry]

This PR adds the ability to pass a list of acronyms to be capitalized when titleizing a string. It also includes the ability to pass a custom list of small words, which are added to the built-in list.

When ActiveSupport is loaded, titleize now will also respect the acronyms configured in ActiveSupport::Inflector.inflections.acronyms.

[granth]

Thanks! This looks good, and I think I'll merge it with some minor changes.

I'll get Hound to stand down on some of its issues – single quotes for sure.

It also takes care of the languishing #11.

[santry]

Sounds good. I left hound's howls alone since what I added seemed to (mostly) match what I saw in the existing code. If you need me to make changes I'm happy to, or, of course, you can hack it as you wish!