New fractal.Paletted_uint32 struct

fractal.Paletted_uint32 is a paletted image struct
based off image.Paletted, modified to use a uint32
index per pixel rather than a uint8 to allow for much
larger colour palettes.

Can be used in the image.Image interface.

When passed to png.Encode, the resultant png will depend
on the size of the palette:
less than 256 colours:  8bit paletted
less than 2^24 colours: 8bit Truecolor
otherwise:              16bit Truecolor
New fractal.Paletted_uint32 struct

fractal.Paletted_uint32 is a paletted image stuct
based off image.Paletted, modified to store pixels
as a uint32 index rather than a uint8 to allow for
huge colour palettes.

fractal.Paletted_uint32 is compatible with the
image.Image interface

When using png.Encode, the formate of the resultant
png will depend of the size of the palette:
less than 256 colours:  8bit paletted
less than 2^24 colours: 8bit Truecolor
otherwise:              16bit Truecolor