Add disposal and transparent option to enable transparent gifs

[yuyuyzl]

Thanks for your amazing quantize & encoding code example!
I'm going to use this in my personal projects, and I will generate some gifs with transparent background.
Here is the result:

[sole]

That's great, thank you @yuyuyzl !

Can I ask who is the author of the images you used for the test? Just trying to not get into licensing issues. I am not familiar with the source, but if they're from a manga or similar, would you mind replacing them with a set of images which can be redistributed? See for example where we quote the source of the images in the dithering test: https://github.com/sole/Animated_GIF/blob/master/tests/dithering.html#L20

[yuyuyzl]

That's great, thank you @yuyuyzl !

Can I ask who is the author of the images you used for the test? Just trying to not get into licensing issues. I am not familiar with the source, but if they're from a manga or similar, would you mind replacing them with a set of images which can be redistributed? See for example where we quote the source of the images in the dithering test: https://github.com/sole/Animated_GIF/blob/master/tests/dithering.html#L20

ok, i changed the demo images to the original ones