Comply with PSR-2 and Symfony convetions

Coding style is changed to comply with:
- [PSR-2 conding style](http://www.php-fig.org/psr/psr-2/)
- [Symfony Coding Standard](http://symfony.com/doc/current/contributing/code/standards.html)
- [Symfony Naming Convetions](http://symfony.com/doc/current/contributing/code/conventions.html)

Resolves #13.

Previous interface is left, but deprecated. Tests for deprecated methods
are also left so the old interface is kept valid unless explicitly
decided to be removed.