Add traits for color schemes from traditional color theory

[Ogeon]

This adds traits for the complementary, split complementary, analogous, triadic and tetradic color schemes. A trait for the complementary color was requested in #383, but all of these may be useful.

[codecov]

Codecov Report

Attention: Patch coverage is 82.52033% with 43 lines in your changes are missing coverage. Please review.

Project coverage is 81.94%. Comparing base (c54efbd) to head (479beec).

Files	Patch %	Lines
palette/src/macros/color_theory.rs	76.00%	24 Missing ⚠️
palette/src/serde/alpha_serializer.rs	24.00%	19 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #384      +/-   ##
==========================================
+ Coverage   81.82%   81.94%   +0.12%     
==========================================
  Files         113      115       +2     
  Lines       18068    18277     +209     
  Branches    18068    18277     +209     
==========================================
+ Hits        14785    14978     +193     
- Misses       3125     3141      +16     
  Partials      158      158              

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[codspeed-hq]

CodSpeed Performance Report

Merging #384 will improve performances by 11.42%

_{Comparing color_theory (479beec) with master (c54efbd)}

Summary

⚡ 1 improvements
✅ 44 untouched benchmarks

Benchmarks breakdown

	Benchmark	master	color_theory	Change
⚡	matrix_inverse	271.1 ns	243.3 ns	+11.42%