v0.5.0

• Added support for Python 3.6.
• Dependencies updated and relaxed, now Django 3 is allowed.
• Testing framework improved to run on 3.6, 3.7, 3.8 with Tox.
• Client setup documentation (Python, GraphiQL) improved. Thanks to
  Rigel Kent.
• Error logging added to simplify debugging, error messages improved.
• Fixed wrong year in this changelog (facepalm).
• Configuration management made slightly simple.
• Bandit linter removed as useless.
• More instructions for the package developers in the README.md added.