Fix Date deserialization without python-dateutil

fixes #79
Merge branch 'malexer-patch-1' into dev
Use more direct type checking in tests

The tests did not catch #79 because datetimes are an instance
of `datetime.date`. From now on, use:
    assert type(obj) == expected_type
Fix error message in from_datestring
Update changelog and add @malexer to AUTHORS
Fix _postprocess call in extending doc
Merge branch 'Ch00k-fix_extending_doc' into dev
Add @Ch00k to AUTHORS
Autodoc SKIPPABLE_FIELDS
Add QuerySelect and QuerySelectList fields
Add QuerySelect and QuerySelectList tests
Add QuerySelect and QuerySelectList tests
Add QuerySelect and QuerySelectList to __all__
Minor tweaks to the docstrings
Add Dummy model
Make QuerySelect related tests more atomic
Use new theme based on alabaster
Update dev requirements
Merge branch 'docs-update' into dev
Make QuerySelect related tests more atomic