Idea: refactor Robyn & SubRouter

[dave42w]

A couple of things bother me about Robyn and SubRouter.

First, this is a lot of code to have in init.py If 686 lines were the whole package then it makes sense But this is two large classes plus (somewhat randomly) the ALLOW_CORS function with loads more code not included in this file.

I'd like to move these out to other modules (which won't change the developer experience as we control that in init.py), robyn.py would be the obvious module name but it's not available. Maybe into robyn_classes or robyn_app

Also, I think we need a RobynBase as a common superclass for Robyn and SubRouter. This way we don't have things like start and inject_global as part of SubRouter where they absolutely should not be called. This gets us on the way to more cleanly nest subrouters to any depth.

What do you think?