Add limits when querying SQL properties
Implemented Cassandra timeseries and discovery support
Changed behavior of sets to store all values
Remove per-series delete in tests due to limitations in
Cassandra counters https://wiki.apache.org/cassandra/Counters
Removed vestigial tests in count and gauge helpers
Added value type support to Cassandra
Added table naming support to Cassandra and SQL backends. Fixes #32.