Fix #65
Store field name and instance on raised exceptions when strict=True

resolves #63
Fix accessing dictionary values when keys are a method of dict

fixes #62
Bump dev version and update changelog
Nested(many=True) serializes None to an empty list

also fix flake8 error in tests
Update docs for fields.DateTime default format
Add length validator
Merge pull request #67 from ewang/dev

Update docs for fields.DateTime default format
Add length validator unit tests
Add ranging validator
Add ranging validator unit tests
Merge branch 'philtay-dev' into dev
Add @ewang and @philtay to AUTHORS
Merge branch 'dev' of https://github.com/sloria/marshmallow into dev
Change many to be passed around
Improve length and ranging validators
Add equal validator
Add equal validator unit test
Add regexp validator
Minor fix