Turn textplay into a gem!

Didn't take as long as I thought it would, so here's the PR for #5.

A couple things I need from @olivertaylor: 

* The gem should have a license. I put in the MIT license because that's the standard for gems – if you have something else in mind feel free to swap it out.
* I've commented a couple places where you should add your information (email, name, etc)
* If you haven't pushed a gem before, I'd be more than willing to push it and then add you as an owner to the gem on Rubygems so you have push access.