Added random-data tests for assoc/dissoc/get/has

In order to do quick-check-like things without waiting for an
implementation, used a very crude object generator
(from ./benchmark/gen-data - although it should probably be moved.

Has resulted in finding, and fixing, quite a few bugs.  I can now
while-loop over the test suite for a good 5 minutes without a
regression.  big steps!
0.2.1 - fixed lots of bugs :D