Add Music21.

EXAMPLES

@@ -85,6 +85,7 @@ Documentation using the sphinxdoc theme
 * Fityk: http://www.unipress.waw.pl/fityk/
 * MapServer: http://mapserver.org/
 * Matplotlib: http://matplotlib.sourceforge.net/
+* Music21: http://mit.edu/music21/doc/html/contents.html
 * MyHDL: http://www.myhdl.org/doc/0.6/
 * NetworkX: http://networkx.lanl.gov/
 * Pweave: http://mpastell.com/pweave/