API guidelines doc

This is super in-progress. A lot of this information is sort of tribal knowledge, but I wanted to get it in out in the open and us on the same page.

This should give us somewhere to look when we're like "how should I name that method/event?", or "how do I doc a method that takes a callback that takes an options hash."
That's currently our plan. We want to deprecate `workspaceView` and have all access go through the model to eliminate the confusion of which to use. If you absolutely need a view object (which you should only need if you need to do unsafe things to the DOM) then you'll call `workspace.getView(model)` to get the view corresponding to the model.