Support running code from GitHub

[3noch]

The codeworld-api package plus the amazing Haskell IDE in VSCode means there is a fantastic local development story for CodeWorld. But I'd still like the ability to share my creations with others. Ignoring complex issues like dependencies, Code.World could allow GitHub to be an alternative storage provider of source code. Sharing the runnable program could be as simple as using a URL with a GitHub link in it.

[cdsmith]

I have no objection to this. I suspect it could be implemented entirely on the client. See https://github.com/google/codeworld/blob/master/web/js/codeworld.js#L297 for the existing code that loads a hash from a URL. You could presumably add a new hash style and load the source from GitHub instead of the CodeWorld server. In fact, perhaps you could allow code to be loaded from an arbitrary URL.