This branch introduces some important SQL optimizations, which drastically reduce the number of database records required for sites with a large number of terms and roles. The admin interface has been updated to allow you to keep your access rules lean and mean.
The changes should ease administration, make some queries faster, and have certainly made the code simpler. The important stuff seems to be working, but please test your rules carefully and report any anomalies (include a simple example of an access scheme which doesn't behave as expected so that we can replicate).
There is an upgrade path from the old version, just make sure that you carefully examine the rules for each role and remove all the extra rules after upgrading.
The documentation hasn't been updated yet (I think a handbook page with lots of examples would be enormously helpful). The basic change is the addition of a global default rule and then a per-vocabulary default for each role which give the permissions for any term which don't have its own rule. More to come (please file issues with questions etc).
The admin UI will likely continue to be improved in this branch.