0.5.0

• depot.io.boto3.S3Storage now provides support for accessing S3 with boto3.
  The previously existing depot.io.awss3.S3Storage can still be used to store
  files on S3 using boto.
• SQLAlchemy integration now handles deletion of files on rollback when session
  is not flushed. Previously flushing the session was required before a rollback too.
• It is now possible to run tests through tox and build docs through tox -e docs
• DEPOT is now tested against Python 3.6