Add json_module class Meta option

Also bump version 0.5.4-dev
Fix py33 test
Test against Python 3.4 with tox
Switch to pytest

For better cross-python testing
added required fields flag, fixes #16
Merge branch 'dev' into DeaconDesperado-required_fields
More complete tests for required field
Fix py3 tests
Update tests
Test against pypy
Update docs
Split serialization and utils tests
Update version and changelog