Added a test that checks that one-time events (once()) work without messing up other events.  Also cleaned up formatting here and there.
Fixed a bug where one-time events (once()) would clobber all other callbacks for the same event if no context was given.  Also fixed a bug in trigger() where it was using off(events...) instead of off(event...) (a typo, really).  The second bug is mostly inconsequential (it would still work--just wasn't proper).