fixing script issues
Updated the database model.

- Added SerializableDate class to customize handling of bson <-> python
- Updated sructure to use SerializableDate class
- Updated hashes to use nested document structure
Updated filtering to use projections instead of client filtering.
[Issue #54] Implemented /cves/algorithm/arg endpoint and tests
Minor fix to correctly reflect structure of 'cves'.
Merge pull request #53 from abn/mongo-delta

Updated filtering and Added cves/ endpoint