simplification for spacesaver. before buckets were kept in an option structure called bucketsOption to defer their computation if not needed. upon a more careful look it turns out this is not very often. the idea that buckets does not have to be calculated in case of repeated merges of SSManys was the original main motivation (since this is what a hadoop reducer will do), but the merge depends on min which depends on buckets in almost all situations, so bucketsOption doesn't help us much here. bucketsOption can be hurtful if an SSMany gets serialized and deserialized, since in that case the None gets serialized and buckets has to be recomputed if needed after deserialization.
Dynamic Summer Addition
Don't use the built in CMS, mutable local one with synchronized around it for perf
Dynamic summer to support configuration options and tested/benchmarked harder.

Have options to decide what should be a HH, if we should reset our metrics, and what frequency to update the mutable state
Moved some code around, added some comments regarding threading. Cleaned up types
remove comments with old assertions
Remove the 1% comment, not useful.

Move the key type to be an Int rather than a Long
Clean up the dynamic summer code a bit
Merge remote-tracking branch 'origin/develop' into feature/dynamicSummer

Conflicts:
	algebird-util/src/main/scala/com/twitter/algebird/util/summer/AsyncSummer.scala
merge from develop
Renamed dynamic summer to HeavyHittersCachingSummer
Merge pull request #314 from twitter/feature/dynamicSummer

Dynamic Summer, may use heuristics to decide not to keep a tuple in a buffer for aggregation.
Merge pull request #308 from tresata/feature/spacesaver-simplification

simplification for spacesaver. before buckets were kept in an option str...
Bump version number, algebird dep. Space saver changed by auto-formatter. Update changes
Merge branch 'release/0.7.0' into develop