Composer Support

A few highlights:

 * Prepared for composer support
 * Split classes into files and made autoload'able
 * Fixed assumption that `$_ENV['GATEWAY_INTERFACE']` was available
 * Fixed `$this->data` being set incorrectly in `RpcException`
 * Conformance was made more verbose*

Conformance was the one thing I'm pretty sure I've mucked up. I know it's not comparing to the last few params of the file. I did include the conformance files since, without the other repos and such, it's not runable.

This is a WIP pull request and very much open for discussion as I don't really consider it "done". Just wanted to get it exposed to @coopernurse