Pyodide 0.20.0 release

Pyodide 0.20 is a major release focused on improving our system for building and packaging Python modules.

We upgraded to Python 3.10. This comes with a speed boost of around 15% in Firefox and 22% in Chrome.

We updated almost every package to the most recent release, and moved closer to using upstream Emscripten. Pyodide 0.20 also includes many small bug fixes and usability improvements.

For the complete list of changes see thechangelog.