Merge branch 'release/0.3.1'
Merge branch 'release/0.4.0'
Merge branch 'release/0.5.0'
Migrating these out from summingbird to more general location
Add tests, fix some bugs. Function name/style refactoring
Remove some debugging code
Hll optimizations
Migrate to newer Caliper, add a HLL benchmark
Optimize the storage backend used in sketch map
Merge pull request #297 from twitter/newer_caliper_HLL_benchmark

Newer caliper hll benchmark
Merge pull request #299 from twitter/feature/HLL_optimization

Optimize HLL sumOption
Remove unused variable
Merge pull request #301 from twitter/sketchmap_opti

Optimize the storage backend used in sketch map
Merge pull request #296 from twitter/feature/migrateAsyncSummersFromSB

Feature/migrate async summers from sb
Have the tests do operations in parallel to stress that better, remove some println's from the code
Use an array buffer rather than list buffer for the map sum
Simple keep a mutable map around, synchronizing access
Geeking out to get the performance higher
Benchmark for the Async summers
Keeping the notion of lazily calculated heavy hitters, but fixing it to actually be a lazy val