Composer support

Adjusted the autoloading to use your autoloader.
Added more info on the package.
Added README instructions
Added php 5.4 constraint

**Steps needed from Facebook**
This package still needs to be added to Packagist, for this please visit: https://packagist.org/packages/submit
Create an account and add this repo's address, the rest is all good. I do recommend that you tag a stable release once its ready, right now the package is flagged as `dev`