Confused Carols - 4 Dec 24 Update

Added 13 new puzzles, 2 easy, 7 medium, 4 hard.  Four are classic Christmas carols and the remainder classical music often associated with Christmas.

Added two new instruments based on modelling a plucked string.  This is somewhat based off of the tech demo, Pluck.  The resulting wave form is just an offset triangle wave, but breaking it down into component frequencies and applying decay proportional to the frequency creates a much better effect than my previous notes.  Unfortunately I'm starting to run up against what can be reasonably synthesized on the fly in javascript (the chords in Jesu, Joy of Man's Desiring and Carol of the Bells cause a noticeable delay in playback).

Also, the updates from the previous release of Mixed Music have been rolled in.  Most significantly, there's a new "Music Box" instrument and the algorithm for swing tempo is improved.  More details can be found in the update notes.