Thanks for the answers - looking forward to the updates and will post on github if I stumble upon some bugs (or come up with some small feature requests) :)
In the meantime - is there a way to music from external source (like an mp3 or ogg file)?
There's nothing in Bitmelo specifically that can do it, however you might be able to get it working using the browser webaudio api. The files would have to be hosted somewhere else, and I haven't tested it out. It might not work though because the game is running in a sandboxed iframe.
https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_API/Using_Web_Audio_A...