Implements a Timeseries.bulk_insert API and an optimized implementation
for Redis and Mongo. Includes support for passing a list of values into
Timeseries.insert. Also includes support for the caller to manage their
own Redis pipelines, finally addressing #12. Some refactoring of the
Cassandra implementation to DRY things up.
Merge pull request #41 from agoragames/batch-insert

Bulk insert