Use native storage for list, map, and bool
Adding support for multiple validation checks
Support easy non-null checks
Fixing serialization of datetime and date types
Updating changelog
Fixing tests for python 3
Adding docs for field validation checks
Simplify index-selection code
Moar tests, moar code coverage
Bump version: 0.3.0 → 0.4.0
Merge tag '0.4.0'