Improved performance, started implementing support for PSR-*

List of changes:

* Started reformatting code to be PSR-2 compliant
* Created a new PSR-4 compliant autoloader
* Started implementing namespaces
* Added unit tests with PHPUnit
* Fixed some performance issues
* Dropped support for PHP <= 5.2 (People can still download older releases for older PHP versions)
* Stopped using submodules as they can cause problems and are not appropriate for a PHP Library, industry best practice is to use Composer

Things to do:

- [ ] Create a new release (proposed: 0.7.0)
- [ ] Rename ``dev`` branch to ``develop`` to use the best practice and be compliant with the rest of the git community