All tests passing. Approx distinct much faster than exact (8 vs 12 s)
Added test for distincts in mixed mode (threshold=5000)
Dialled back version number as otherwise we'd skip 2.X completely ;-)
"test" scope for jsonassert, to reduce package size
Removed Trove as we're only using ES's own cache-friendly version
Wrote a timezone rounding cache, but it's actually slower :-(
Big speed boost for approx distincts by tuning CountThenEstimateBytes