Add option to use real Lego colors

[kpalmvik]

It should be possible to specify that transform() should only render bricks in the official Lego brick colors (http://lego.wikia.com/wiki/Colour_Palette)

This is probably tricky to do using the current implementation, and may require some additional image processing.

See JuanPotato/Legofy#2 for reference.

[Wildhoney]

Agreed that it should definitely be possible — others have also mentioned applying dithering and then setting up a LEGO shopping basket with the bricks that make up your image.

Will look into this one 👍

[Wildhoney]

In fact looking at the quantize library RgbQuant, this should be able to do it for us using the palette option.