Feature importance

[yufongpeng]

Clean commits from #166

[codecov-commenter]

Codecov Report

Merging #182 (3d0f314) into dev (be7a715) will increase coverage by 0.20%.
The diff coverage is 93.13%.

@@            Coverage Diff             @@
##              dev     #182      +/-   ##
==========================================
+ Coverage   89.34%   89.54%   +0.20%     
==========================================
  Files          10       10              
  Lines        1004     1177     +173     
==========================================
+ Hits          897     1054     +157     
- Misses        107      123      +16     

Impacted Files	Coverage Δ
src/util.jl	92.18% <ø> (ø)
src/DecisionTree.jl	51.51% <57.89%> (-3.59%)	⬇️
src/regression/main.jl	92.00% <88.23%> (-2.74%)	⬇️
src/measures.jl	97.23% <95.74%> (-0.42%)	⬇️
src/scikitlearnAPI.jl	50.42% <96.42%> (+10.83%)	⬆️
src/classification/main.jl	97.89% <98.83%> (+0.27%)	⬆️
src/abstract_trees.jl	100.00% <100.00%> (ø)
src/classification/tree.jl	100.00% <100.00%> (ø)
src/regression/tree.jl	100.00% <100.00%> (ø)

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[ablaom]

Looks good to me.

@yufongpeng Thanks for this substantial contribution.

[yufongpeng]

Thanks for the opinions on this PR. l'm happy it is finally done!