Maturity bump to 1.0

New features

• none!

Package changes

• add flake8 config
• convert docs to markdown
• Removed bundled six.py.
• Taken over ownership via PEP451; pypi issue here, successfully contacted Sam.

Tests

• remove sys path hacking from tests.
• Ensure they work now.
• Github Actions are in place for continuous integration.
• Allow longer flake8 line length in tests.