Colors and glow for individual keys in stave notes.

The API is very simple, though I'm happy to make any changes necessary.

    var note_struct = { keys: ["g/4","b/4","d/5"], duration: "q" };
    var note = new Vex.Flow.StaveNote(note_struct);
    note.setKeyStyle(1, {shadowBlur:15, shadowColor:'blue', fillStyle:'blue'});

![Screen shot](https://f.cloud.github.com/assets/20748/510614/893e09ee-bddf-11e2-997c-fa566e9be16b.png)