Expiry auth token model with some tests
Test the token auth process
Add management command to remove expired tokens
Add serializer for the auth token expiry
Tests for malformed auth tokens
py2/3 test compability
[ci skip] Update Readme
[ci skip] Update Readme with info about token expiry times
[ci skip] Explicit value for token times
[ci skip] Update changelog
[ci skip] Fix import order
Merge pull request #87 from incuna/auth-token-expiracione

Token expiration functionality
Split `VerifyEmailMixin` and `BasicUserFieldsMixin` into more mixins.
Move check to EmailVerifyUserMixin
Fix syntax for python2
Move `__str__` and `UserManager` on `NameUserMixin`
Mixin order matter
Update CHANGELOG.md
Fix test with unicode
Simplify test with Python2AssertMixin