Restructure IO handling files.
Add constant for localhost.
Introduce peer_io.h

This file declares the IO specific structure used in struct peer.
Rename io_epoll.c to io.c
Rename io_epoll.c to io.c
Rename io_ops.h to peer_io_ops.h
Move statements that belongs together more closely.
Take out unused include statements.
Remove program to generate message hashes.