Rendering a picture on a plot renders alpha channel incorrectly

[TheQuantumPhysicist]

Using this example: https://github.com/plotters-rs/plotters/blob/master/plotters/examples/blit-bitmap.rs

The problem is that even if the PNG has a transparent background, it's rendered in the plot incorrectly. I dug into this a little bit and I think this is because the BitMapElement doesn't support having alpha channel and it uses RGB instead of RGBA (I saw the image library supports RGBA). I think this is a bug and should be fixed.

To prove the issue exists, simply make a plot, then render a picture above the plot. The picture's rectangle will simply wipe everything under it, even if the PNG has a transparent background.