0.20.0

Supporting async kernel execution in ipykernel>=6 required significant changes to critical path code. Please make an issue if you see errors after upgrading!

What's Changed

• Drop Support for Python 3.6 by @devstein in #755
• Simplify and Speed up Docker Images by @devstein in #756
• Re-format All Code with black. Require black in CI by @devstein in #758
• Support IPython 8 by @devstein in #759
• Support ipykernel >= 6 by @devstein in #737

Full Changelog: 0.19.2...0.20.0