Hi Andy,
first of all, I'd like to say thanks for your contributions so far; I acknowledge -and I'm happy to see- your interest in getting even more involved with the project,
We don't have (yet) a formal process for promoting contributors to committers, but we're definitely going to discuss this topic soon and will get back to you. In the meantime, should you happen to have time for helping on reviewing existing and future PRs from other contributors... well, that's always going to be appreciated (and it helps to increase the knowledge of the codebase).
Cheers