Build binaries for linux-aarch64 and armv7 (e.g. raspberry pi)

[almarklein]

Should be easy to add now.

So I learned that aarch64 does not run on RPi, you need armv7 for that. I think we'd need aarch64-unknown-linux-musl if we want to create a Python binary wheel for wgpu-py.

Tried in armv7 in #148. Lib works, but wgpu not yet. That PR might be a basis for a stab at aarch64 though.