v0.5.1

• Log Protean exceptions to print helpful debug messages
• Support for installation of optional dependencies
• Remove support for Data Transfer Object
• Remove support for Request and Response Objects
• Bugfix - Throw Exceptions on Unit of Work commit failures
• Use black as code formatter with a git pre-commit hook
• Add 3.9 to test matrix and cleanup Travis.yml
• Bugfix - Fix broken Sphinx docs build