luacat: rewrite in Go

[zombiezen]

It's a bit cumbersome to have multiple languages in play in one repository, as it increases load on contributors. Since Lua is the only hard dependency that needs C, then this could be a viable candidate for using cgo. I haven't tried using Bazel's cgo support yet, so doing this may require a bit of experimentation.

[rockwotj]

Should be easier with: https://github.com/yuin/gopher-lua