Added Cassandra 2.0 Compatability

I updated the Blob, Date, and DateTime columns to support the new formats being returned / required for input by Cassandra 2.0. I also modified the get_fields method to support filtering out of non-regular fields, by pulling the whole row and filtering where necessary. This acts as a workaround for needing the version of cassandra, and is the minimal amount of work to get compatible with C* 2.0 without integrating something like python-driver. I've tested this on both C* 1.2.13 and C* 2.0.3, with all tests passing.