VIM Mode

VIM bindings are :chefkiss:

Please, have mercy on my poor wrists and implement them in ``

This could be accomplished by exposing the `codemirror` instance publicly, then I could just [yadda yadda](https://codemirror.net/demo/vim.html) in user land. Or you might decide it's worthwhile implementing this as a Feature™️. Either way, Please consider enabling some form of VIM bindings, if not for my wrists' sake, than at least to give your users something to argue about ;)
I suppose I could just subclass? but that seems an awfully long way to go around just for this feature. Perhaps my perspective on that is limited though.