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."
What about the `will-x` event and `x` event being cancelable? For example the following scenario:

1. The `will-x` event is raised
1. My listener does something in response to the `will-x` event
1. The `x` event is raised
1. In the process of handling the `x` event, it is canceled

Should the "something" in step two be "rolled back"? Or should we say that one can only cancel things from the `will-x` event? Once the `x` starts, it is going to complete unless there's an error.