Major refactor of network code

Major refactor of network code

Here I massively change both the external and internal API of the TCP
sockets and servers.

This change introduces the concept of a protocol object like is found in
Twisted Python. I believe this allows for a much cleaner description of how
a socket behaves. What was once a single object "client" or "connection" is
now represented by two objects: a "connection" and a "protocol".

Well - I don't want to ramble too much because neither API is yet public or
documented.  Look the diff of test/test-pingpong.js to see how things have
changed.