Adding mixed mode estimator.
Minor functions for determining the cutoff points for switching from set
to HLL.
Adding nippy to development dependencies.
Adding coverage support.
A bit of refactoring.
Fixing tests (the cutoff was lowered a bit).
Adding coveralls config.
Updating readme to include the coveralls link.
Added service_name to Coveralls config as per docs.
Fixed a few issues with union.
Minimized test data size a bit to avoid long test times.
Remove debug print.
More test cases.
Better test coverage.
Merge pull request #8 from screen6/mixed-mode-estimator

Mixed mode estimator