Fix RFE n_features minimum value #3812
Fix RFE n_features minimum value #3812 and make it simpler.
If step is explicitly zero or negative, raise a ValueError exception.
ENH Release gil in feature importance
ENH use threading backend for features importance parallelisation
FIX explicit initialization of normalizer
Minor doc enhancement: documented setup develop.
Added link to the setuptools doc and a note on the need to rebuild every time a
compiled extension is modified
Check if targets is a numpy array and convert it into one if it isn't
Merge pull request #3902 from JeanKossaifi/doc_enhancement

Minor doc enhancement: documented setup develop.
reverted css to current stable, fixes the display bug
Merge pull request #3898 from arjoly/nogil-feature-importance

ENH Release gil in feature importance
Merge pull request #3899 from jlopezpena/fix-OvOlist

[MRG+1] Let OneVsOneClassifier use list of targets
DOC "RF" -> "Random forest" in text classif example
Merge pull request #3915 from ThomasDelteil/fix_css_examples

[MRG+1] reverted css to fix display bug in documentation, example page
Replace 'coefs' by 'coef_' in PLSRegression
Merge pull request #3920 from jlopezpena/pls-coef

[MRG] PLSRegression coefs to coef_
various docstring fixes for web docs
ENH do not use plt.cm.jet in JL bound example

Also move the call to plt.show() to the end of the script
to avoid blocking the execution.
DOC fix kernels documentation inconsistencies

Fixes gh-3916, gh-2901.