PSR refactoring

I decided to use your library to test the API that I'm working on at the moment. I manage dependencies in my project using Composer but unfortunately your library isn't available as a Composer package so I decide to contribute to you project.

I made major changes to the codebase to make it compatible with today's standards and what is the most important to make it available via Composer. 

Changelog:

1. Modified structure of the library to be compatible with PSR-4
2. Added composer.json with basic information so that anybody could download it as a dependency via Composer.
3. Added namespace
4. Removed unnecessary required_once statements because now classes can be autoloaded using composer's autoload just by including autoload.php file from the vendor directory : 
include 'vendor/autoload.php';
4. Changed method names to camelCase (PSR)
5. Changed code formatting (PSR)
6. Removed duplicated code (DRY)