[feature request] on_filetype support append so that I don't need add default options each time.

[cxwx]

now

	local augend = require("dial.augend")
	require("dial.config").augends:on_filetype {
	  typescript = {
		augend.integer.alias.decimal,
		augend.integer.alias.hex,
		augend.constant.new { elements = { "true", "false" } },
		augend.constant.new { elements = {"let", "const"} },
	  },
	  lua = {
		augend.integer.alias.decimal,
		augend.constant.new { elements = { "true", "false" } },
	  },
	  markdown = {
		augend.integer.alias.decimal,
		augend.misc.alias.markdown_header,
	  }
	}

need

	local augend = require("dial.augend")
	require("dial.config").augends:on_filetype {
          default = {
               augend.integer.alias.decimal,
               augend.constant.new { elements = { "true", "false" } },
          }
	  typescript = {
		augend.integer.alias.hex,
		augend.constant.new { elements = {"let", "const"} },
	  },
	  markdown = {
		augend.misc.alias.markdown_header,
	  }
	}