Slowly but surely. This project is on hiatus and will resume in 2020.
The best way to submit a patch is to send us a pull request. Before submitting the pull request, make sure all existing tests are passing, and add the new test if it is required.
If you want to add new functionality, please file a new proposal issue first to make sure that it is not in progress already. If you have any questions, feel free to create a question issue.