Guest language support: Zig

[Zig](https://github.com/ziglang/zig/) is a great source language, and shows Wasm a lot of love in [many](https://ziglang.org/documentation/master/#WebAssembly) different [ways](https://ziglang.org/news/goodbye-cpp/). I'd like to be able to use seperately-compiled Wasm components in Zig, so I wanted to open this issue to gauge demand.