Guidelines for contributing

Fork the repository.
Create a topic branch.
Make your changes, including tests for your changes.
Ensure that all tests pass, by running:
```
composer install --dev
cd tests && php all_tests.php && cd ..
```
The Travis CI build runs on PHP 5.3 and 5.4.
It should go without saying, but do not increment the version number in your commits.
Submit a pull request.