This commit adds a behaviour protocol that implements the AutoNAT specification.
It enables users to detect whether they are behind a NAT. The Autonat Protocol
implements a Codec for the Request-Response protocol, and wraps it in a new
Network Behaviour with some additional functionality.
Co-authored-by: David Craven <david@craven.ch>
Co-authored-by: Max Inden <mail@max-inden.de>
