Implement new indexing semantic for StateMonitor, closes #88
Add tests for the new indexing semantics
Replace numpy scalar values with numpy data types with their Python equivalents (e.g. replace np.int64(1) with int(1)) -- weave otherwise treats them as general Python objects, not as numbers
Merge pull request #90 from brian-team/monitor_return_values

Implement indexing semantics for StateMonitor