Colors and glow for individual keys in stave notes.

The API is very simple, though I'm happy to make any changes necessary. Fully tested in canvas, Raphael, and Node.js canvas (on my `colors` branch, from which this was cherry-picked).

    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)