Feature request: add text-shadow props

Hey there, since I started using this framework I always got "stopped" when setting a text-shadow because instead of having the convenience of stepped --shadow-* variables, I always have to "craft" the text-shadow myself. I find them incredibly useful for making text on an image more legible. I feel like it should be as minimal/soft as the normal --shadow values, maybe without an offset, e.g. 0 0 3px rgba(0, 0, 0, 0.5) would be something that I type regularly and that I would like to standardize through the use of this framework.