Create a dynamic tkinter background gradient.
based on this stack overflow answer: https://stackoverflow.com/questions/32530345/pil-generating-vertical-gradient-image/32532502#32532502
Mainly I want to have this available when I try to create more dynamic tkinter displays. Feel free to do whatever you want with it, maybe even make tkinter do moderner graphics. My goal is to make it resize with the window. This is based on the idea that, rather than creating an image, you can create the image data programmatically and stream it to tkinter.