[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.
That's weird, the only place where the misalignment shows up is in this pull, it looks fine locally using less & vim, and looks fine on GH outside of this pull.