Add build variants for other platforms

# Target platforms
## Linux with musl
`x86_64-unknown-linux-musl`

## Linux for ARM64
`aarch64-unknown-linux-gnu`

## Supports Pi 0/1
`arm-unknown-linux-gnueabihf`

## Supports Pi 2/3/4
`armv7-unknown-linux-gnueabihf`

# Source
- https://doc.rust-lang.org/rustc/platform-support.html
- https://chacin.dev/blog/cross-compiling-rust-for-the-raspberry-pi/