issues with PNG alpha channel

[fimkap]

termpix has issues displaying transparent PNG, not sure if support for alpha channel was planned
one such example:
This is how the image looks in MacOS Preview (photoshop will display it with a checkerboard pattern)

this is how it is displayed on iTerm2 with true color on

tried it on Terminal.app, with or without true color - it doesn't help
I'm attaching the original image:

Maybe the solution will be to identify the transparent pixels and build a checkerboard pattern with unicode half-block. Meanwhile, I will have to use imagemagick to compose another image with transparent pixels replaced with the pattern and then to display it with termpix.

[fimkap]

I have added alpha blending in my fork. Now it seems to work well. I have created a pull request.