Add highlight.scm

[theHamsta]

@clason does tree-sitter highlight have any documented guidelines for upstream queries? I tried to follow tree-sitter-cpp, tree-sitter-c. locals.scm/injection.scm could be added following nvim-treesitter

Rust crate needs update for the query constants

Fixes #91

[clason]

@clason does tree-sitter highlight have any documented guidelines for upstream queries?

I am not aware of any. Github added a set of "base captures" to tree-sitter, but that's fan fiction as far as I am concerned. For this org, though, nvim-treesitter queries are the standard, so just upstream those.