Show data in ImageOverlay from memory?

[deeplook]

I've run into this: #120 and while providing relative file paths does work it would be much nicer to read the image data directly from a binary in memory. Also the working solution looks different for Lab and non-Lab. Not sure if Leaflet makes this impossible, but having to save a (generated) file first slows down the process and makes the code more ugly. And running a mini webserver also looks like overkill.