Bootstrap `go-pkg`

[ricochet]

This project will also include go SDK higher-level types, like a wasi-sockets socket implementation or http. These will live under pkg.

• Update README for go-pkg
• Move over vanity, /docs
• Move over wit-bindgen source. /pkg <- migrate wit-bindgen source
• Write release process
  • Single tag for wit-bindgen and higher-level Go modules where we have 1 release for all packages in this repo

Then once we have types here, let's migrate wit-bindgen to use these types. We can use a go.mod that depends on the types here or use a git submodule over in wit-bindgen for the unit tests.