Protocol reference documentation

[cornelius]

We need reference documentation for the peer-to-peer protocol. This is important for people who want to understand how Unit-e works in detail as well as developers who want to work on unit-e or other software which needs to deal with the protocol.

Maybe there it would be good to generate this documentation from information maintained as part of the unit-e source code so that it's naturally maintained and kept up to date and correct.

The bitcoin.org P2P Network documentation might be helpful as a base.

We have an initial import with names adapted to Unit-e in the doc-prototype wip branch but without any further adaptions of the content.

[cornelius]

PR to add the documentation of the P2P messages: #21