`makeRequest` returns the request object, but `get` and `post` swallow it and return undefined.

Would it be useful to return the request upward to callers? Or is it a leaky abstraction asking for trouble? I'm not sure. Either way, we probably should be consistent, as `makeRequest` is part of the exported module API along with `get` and `post`. Your call.

Actually, it looks like we publish the request in the `xhr_start`, `xhr_complete`, and `xhr_delay` signals, so I think `get` and `post` should return `this.request()`? Yay uniformity.