Split Peasy up into raw server and API

[KaneCheshire]

Currently everything is bundled up as one lib which includes the code to handle sockets, and the nice API on top of that to handle intercepting requests and responding etc.

It would be beneficial for the socket stuff to be broken out into a separate reusable lib so that any API can be built on top of it. Peasy's API is nice but may not suit everyone, and also restricts the way that new APIs must be written (for example I've had to really think about the way websockets work and fit nicely with Peasy's existing API).

The socket lib (name pending lol) will essentially be a wrapper around the core Darwin APIs to listen for incoming socket requests, keep them open and handle reading from and writing to a socket.