Add support for nvim-treesitter-context

[rami3l]

Closes #34 by adding a new entry for the key TreesitterContext to the color table.

Tested with the following override configuration:

  {
    "Shatur/neovim-ayu",
    name = "ayu",
    config = function()
      local ayu = require("ayu")
      local colors = require("ayu.colors")

      local mirage = true
      colors.generate(mirage)

      ayu.setup {
        mirage = mirage,
        overrides = {
          TreesitterContext = {
            bg = colors.selection_inactive,
          },
        },
      }
    end,
  },

[Shatur]

Thanks! But could you also attach a screenshot?

[rami3l]

Thanks! But could you also attach a screenshot?

@Shatur Sure! It looks like this on my machine: