[RFC] Misc. msgpack-rpc doc fixes

Hi,
I'm not totally sure what this project's guidelines are in regards to docs, but most of these are pretty simple changes so I'm copefully complying by them.
I've signed the CLA, and I believe this should supersede #1352.
Technically this should be `viz.` but that would be too pedantic for software documentation purposes. I think the colon should be preserved though.