color: add `CMYK` support

[rabsef-bicrym]

See here for an algorithm.

Requirements:

• Add %cmyk to get and ned, where appropriate.
• Develop a type for get that makes sense with the needs of CMYK format
• Write conversion functions CMYK <-> RGB and then use extant functions to pad other color-formats when starting with CMYK (see HSL start, Hex start).
• Add cmyk to all's output and fix lo-abet to produce it.