wireproto: implement basic command dispatching for HTTPv2
Now that we can ingest frames and decode them to requests to run
commands, we are able to actually run those commands. So this
commit starts to implement that.
There are numerous shortcomings. We can't operate on commands
with "*" arguments. We can only emit bytesresponse results. We
don't yet issue a response in the unified framing protocol.
But it's a start.
Differential Revision: https://phab.mercurial-scm.org/D2857
(binary:application/octet-stream)