Add support for go.mod files

[camdencheek]

This commit adds a grammar for go.mod files using the definition found
at https://golang.org/ref/mod#go-mod-file-grammar.

I did my best to imitate the multi-grammar repos for typescript and ocaml, but I may have missed some things.

I've been using this through nvim-treesitter (screenshot below), so I haven't exercised the other bindings.

[maxbrunsfeld]

This is great work @camdencheek. I actually think that the mult-grammar repository structure of tree-sitter-typescript and tree-sitter-ocaml is a bit cumbersome, and it's only worthwhile to me because those grammars share some common code. For example, in TypeScript, the typescript and tsx grammars share some common grammar code, queries, and tests.

In this case, since go.mod and Go are two completely different languages, and some users may only care about Go, but not go.mod, I would prefer to just keep the go.mod grammar in its own repository. What do you think about that?

[camdencheek]

Seems reasonable to me! I'll go ahead and pull it out into a separate repo.

What are your thoughts on this being a personal repo vs under the tree-sitter org? I don't see anything in the contribution guide about contributing new grammars. I'm happy to maintain it either way.

[camdencheek]

Closing in favor of implementing the go.mod grammar in a separate repo. New repo is at https://github.com/camdencheek/tree-sitter-go-mod

[maxbrunsfeld]

Yeah, I think a personal repo is best. Do you want to open a PR on tree-sitter/tree-sitter that adds a link to your grammar in the docs (here)?

[camdencheek]

Done 👍