* Remove `LoopData` as it's no longer necessary
* Add `LoopHandle::spawn` to spawn new futures onto an event loop
* Add `LoopData::spawn` to also spawn new futures onto an event loop
* Rejigger the implementation of the event loop a bit (make a slab of futures),
but otherwise everything else is pretty constant.
Split it up into a number of targeted modules for each purpose, for example loop
data, I/O sources, timeouts, and channels. No actual change is intended to be
part of this commit.
Alex Crichton