Proxy EventLoop

[AustinSchuh]

Originally from @bsilver8192

An EventLoop implementation which creates multiple EventLoops that are all scheduled via one underlying EventLoop would allow combining multiple applications in a single process. They must all be on the same node, and can communicate with each other and the outside world as normal. This would provide a similar API to SimulatedEventLoopFactory which can create new EventLoops on demand.

Some tricky things to keep in mind:

• Make sure watchers and senders from all the proxied EventLoops work with each other
• Multiple senders on the same channel in multiple proxied EventLoops. TimingReports end up doing this.
• Timers and fetchers can mostly be used directly. Should tack on something in the name to help decipher TimingReports though (each one will be reported twice, once with a longer name in the proxy EventLoop and once with just the given name for the proxied EventLoop)