Merge pull request #2 from shawnohare/fix/remove-deprecated-ts-hl-groups

Deprecate use of neovim 0.7.2

Replace neovim 0.7.2 treesitter highlight groups of the form `TS<X><Y>`
with the neovim 0.8 analogs of the form `@x.y`.

Implement the suggested lush method for defining these groups
as per rktjmp/lush.nvim#109

Fixes #1