Stable releases for x64 Linux, MacOS and Windows.

This release contains numerous colour quantization improvements and new options.
It also contains 256x384 Gigascreen interlaced resolution support by request.
Note that interlacing skips lines/places them on the same pixel row so the output may be of lower quality than a standard resolution 256x192 Gigascreen image because the dither pattern height is halved.

Technically I consider 256x384 interlace to be inferior to true 256x192 because it's impossible to accurately represent the palette of two pixel rows, each using their own 4 colour (Gigascreen attribute) palette, into a single 4 colour palette - the pixels end up merged (and do in this implementation).
Please don't have the idea this is the same as your old school 1:1 Amiga interlace modes - that machine did not have palette restrictions that required colours to be within a set of 4 every 8x8 pixels.