MAINT: Lint all the things

Upgrade to emscripten 1.38.12

Use constant hiwire ids for singleton values

No need to copy bound method name

Refactoring common functions under pyodide_build

Use "BINARYEN_TRAP_MODE='clamp'"

Disable sigaction and utimensat syscalls

This reverts commit 3ff79f6a.

Add test for iterating over a JS array

Add a hard-coded pyconfig.h

MAINT: Remove old if statement that's always True

Fix LZ4 decoding bug

This was introduced in #170, but wasn't caught since emsdk didn't get rebuilt

Add API reference documentation

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