JAMS v0.2 is full of improvements which make it easier to work with, as well as easier to extend. You can read the full technical report here:
B. McFee, E. J. Humphrey, O. Nieto, J. Salamon, R. Bittner, J. Forsyth, J. P. Bello, "Pump Up The JAMS: V0.2 And Beyond", technical report, October 2015.
Or, if you'd like to dive right in, head straight to the JAMS GitHub page.