internals: refactor wire protocol documentation Upcoming work will introduce a new version of the HTTP and SSH transports. The differences will be significant enough to consider them new transports. So, we now attach a version number to each transport. In addition, having the handshake documented after the transport and in a single shared section made it harder to follow the flow of the connection. The handshake documentation is now moved to the protocol section it describes. We now have a generic section about the purpose of the handshake, which was rewritten significantly. Differential Revision: https://phab.mercurial-scm.org/D2060