MIDI: First attempt at a shim, and a few issues filed

Hey gang-
I slammed out a first attempt at a Web MIDI API shim running on top of the
Jazz NPAPI/ActiveX plugin, and as I was coding it ran across a few issues
that I just filed in Bugzilla.  The shim is on Github, at
https://github.com/cwilso/WebMIDIAPIShim.

This was mostly so that I will start building my own MIDI demo apps on top
of something that looks more like the Web MIDI API, rather than the direct
Jazz interface.  :)

-Chris