Customized colors

[wangjiawen2013]

Now can set boxplot colors, it's useful when plotting grouped boxplot, because we need use different colors to label the different groups.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 83.60656% with 10 lines in your changes missing coverage. Please review.

Project coverage is 99.61%. Comparing base (1f2987a) to head (4216a2a).
Report is 77 commits behind head on main.

Files with missing lines	Patch %	Lines
src/boxplot.rs	83.60%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #86      +/-   ##
==========================================
- Coverage   99.68%   99.61%   -0.08%     
==========================================
  Files          19       20       +1     
  Lines        5132     5456     +324     
==========================================
+ Hits         5116     5435     +319     
- Misses         16       21       +5     

Flag	Coverage Δ
	99.61% <83.60%> (?)

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[cpmech]

Hi, thanks for the PR. It's now published.