From 38.479 to 24.067s.
No improvement. :(
Improvement by some milliseconds.
Down to 0.209s!

In theory the implementation is less efficient, but numpy is like
always faster than implementations in Python.
Delete _searchsorted_pairwise. Not needed anymore.
Optimization clean-up.
More performance and numerical stability.
Remove tests for no longer existent function.
Fix problem if not a Quantity.
Improve performance of van Rossum metrics.

Speed-up factor up to around 1000!

Merge branch 'feature/vr_perf' into feature/stMetrics