Treesitter support

[YodaEmbedding]

Colors for treesitter highlighting coming in Neovim 0.5.

Though if the changes are non-trivial, perhaps it would make sense to make a new plugin "nvim-treesitter-quantum" instead.

[cloudlena]

Since there was no response to my PR, I created the fork https://github.com/mastertinner/nvim-quantum which is completely written in Lua and based on Tree-sitter.

[YodaEmbedding]

Neat. I've been using tokyonight.nvim (Storm), which has many similarities to quantum, but it might be nice to switch back to a quantum theme.

EDIT: Looks great. I do miss the higher contrasts of tokyonight, but luckily, the color palette can be tweaked with a few changes to these 13 constants. It might be a nice idea to expose these as overridable in the config.

[cloudlena]

Tokyo Night is gorgeous indeed. Thanks for the hint!