[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.
Should I apply spacing before all parentheses? I didn't as I saw that there were no spaces before any of the parens I saw, but think it looks  better.