Feature request: display in-memory images without disk roundtrip

[qwenger]

Thanks for the very nice library.

I'm generating some images on-the-fly and displaying them in easygui to ask the user for input for further processing. It feels wrong to have to save those images to temporary files to be able to display them, as I already have them loaded with pillow.

It would be nice to be able to submit not only image file paths but also pillow images as image arguments.