Web MIDI spec updates

Hey, I just committed to my editing branch -
https://github.com/WebAudio/web-midi-api/tree/cwilso-edit - changes that,
among other things, include the full hooks for Promises and a revision of
the inputs and outputs to a MapClass-like system.  I can't figure out a
good way to host this semi-officially; as it is an editor's draft, I'd like
to simply push it to the main gh-pages branch.  Any objections (Jussi, I'm
specifically looking for your approval, of course)?  Otherwise, please
review the draft in the Github repo (you can pull it out and load it from a
local file, even).  I'd like this to be in the source for the next public
WD.

-Chris