add new selector based on information gain

[solegalli]

FYI @Morgan-Sell

closes #488
closes #280

[solegalli]

Still need to fix some errors, and go over the documentation

[solegalli]

Hi @Morgan-Sell

I just fixed the last bugs and went over the documentation. You did an awesome job with the user guide and the docstrings. Thank you so much!!

[codecov]

Codecov Report

Merging #542 (57e444f) into main (07de62b) will increase coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #542      +/-   ##
==========================================
+ Coverage   97.41%   97.47%   +0.05%     
==========================================
  Files          89       90       +1     
  Lines        3410     3480      +70     
  Branches      673      681       +8     
==========================================
+ Hits         3322     3392      +70     
  Misses         32       32              
  Partials       56       56              

Impacted Files	Coverage Δ
feature_engine/selection/target_mean_selection.py	97.05% <ø> (ø)
feature_engine/encoding/woe.py	100.00% <100.00%> (ø)
feature_engine/selection/__init__.py	100.00% <100.00%> (ø)
feature_engine/selection/information_value.py	100.00% <100.00%> (ø)

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[solegalli]

reopening, because I seem to have forgotten to merge!