nakamoto-net-mio

This crate is a nakamoto network reactor implemented using the mio library. It is a drop-in replacement for the default nakamoto-net-poll crate normally used with nakamoto. The reason to use this over nakamoto-net-poll is purely for better cross-platform support. At the moment nakamoto-net-poll is based on popol which is a minimal wrapper around poll(). I believe popol will only work on unix based systems.