Add CAM16 color spaces and HCT, also add related ∆E, gamut mapping, and contrast algorithms

[facelessuser]

Add CAM16 color spaces and HCT, also add related ∆E, gamut mapping, and contrast algorithms

• Add CAM16, CAM16 JMH, CAM16 UCs, CAM16 SCD, CAM16 LCD
• Add ∆Ecam16 and ∆Ehct
• Add HCT Chroma gamut mapping to produce proper tonal palettes
• Add Lstar contrast
• Add new achromatic_hue method to Cylindrical color spaces to return the proper hue for achromatic translation (usually zero, but some, like CAM16, require something other than zero for best results.
• Better detecting of achromatic hues in some cylindrical spaces.

Resolves #255, Resolves #212

[facelessuser]

@gir-bot lgtm