Add API reference documentation

WIP: Use LZ4 filesystem compression, using the canonical C implementation

Fix load .data files from the same base URL as .js

Add dev python notebook python_dev.html

Simplify traceback on package load timeout

Use Firefox latest, rather than nightly, for testing

Reorg pyodide ns to separate emscripten details from public API

MAINT Refactor test web server to allow multiple instances and log capture

Guard against infinite recursion when converting self-referential data structures

MAINT: Use bitwise and rather than mod, for performance