Contribute source code

Short how to:

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Add tests for new functionality
4. Make sure that it does not break anything
5. Review your code
6. Commit your changes (git commit -am 'Add some feature')
7. Push to the branch (git push origin my-new-feature)
8. Create a new Pull Request