feature: janet shell

[jerivl]

Hi! This is a really exciting project. Thanks for your work on it so far.

I'm unsure if this is already possible, but a shell or repl of some kind to run janet code within a server would be helpful for e.g. hot-edits of layouts, etc. This would also improve scripting workflows.

[cfoust]

Hey there! This is a great idea. I've been meaning to expose the standard Janet REPL in cy. Honestly, testing configuration changes is not great right now, either! There's room for improvement there. Thanks for trying out the project and please feel free to send me feedback!