Mods to handle generation of min/max aggregations in-memory.  It will attempt to read the relevant aggregation bin from Cassandra once (during a startup situation, etc) and all other agg state is handled in memory.
Added requested test.
Merge pull request #28 from esnet/aggs_in_memory

Mods to handle generation of min/max aggregations in-memory.  

It will attempt to read the relevant aggregation bin from Cassandra once (during a startup situation, etc) and all other agg state is handled in memory.