Add support for vlang filetypes.
- [ ] Highlight `C` as builtin variable. This is FFI in vlang land,
where C act like extern and access c functions. The vlang parser does
some extension between C function calls and arguments but I believe
highlighting C as builtin variable is sufficient indicator for now. I
tried to use offset! but failed. Any suggestions?
- [ ] Set up parser url. the vlang parser is located within [vls] repo. Is
installing from nested repo supported? `tree_sitter_v/src/parser.c`?
[vls]: https://github.com/vlang/vls/tree/master/tree_sitter_v
cc @elianiva @theHamsta
