Event loop and event-driven async socket base class
This is an abstract base class for objects backed by a socket which provides the basic framework for event-driven asynchronous IO, designed to be fast. Danga::Socket is both a base class for objects, and an event loop.
Callers subclass Danga::Socket. Danga::Socket's constructor registers itself with the Danga::Socket event loop, and invokes callbacks on the object for readability, writability, errors, and other conditions.
Because Danga::Socket uses the "fields" module, your subclasses must too.