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

revlog: rename 'self.checkinlinesize' into '_enforceinlinesize' The name change has two motivations: 1) The function has no external caller, so we move it to protected space. 2) the function does more than checking it also split the data if we have more data than 'inline' supports.

revlog: add a _datareadfp context manager for data access needs The helper handles: 1) is there a file handle already open that we shall just reuse, 2) is the revlog inlined or not. Using a context manager for all read access will help setting up file pointer caching in later changesets.

revlog: use context manager for data file lifetime in checksize This is clearer, safer and more modern.