Official composer support

Hey Jason,

You don't have issues enabled so this seemed like the simplest way to reach out to you. 

I wanted to let you know that we finally got around to adding composer support and an official package (https://packagist.org/packages/recurly/recurly-client). After I'd published it I noticed you also had a package so, I did want to say thanks for taking the initiative to get a copy of our client up on Packagist.

I've been trying to spend more time on the PHP client so hopefully things like this won't languish going forward. If you have other ideas or improvements please let me know.

andrew