Support also treesitter colors

Created by: mcepl

neovim developers work hard now on support treesitter (see supporting project https://github.com/nvim-treesitter/nvim-treesitter, but the main support is directly inside of the main source tree), I am not an Emacs user, so I am not sure with the situation there, but at least there is emacs-tree-sitter package (now on MELPA).

There is some documentation in neovim doc file and there seems to quite an interest in it on Reddit, but I am not exactly sure what exactly it means for the color schemes like this project.

This discussion seems to be relevant.