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.
Merge pull request #3869 from borjaayerdi/rfe_n_features_to_remove

Fix RFE n_features minimum value #3812
DOC more expansive description of well-established algorithms
DOC typo
ENH LinearSVR using liblinear code

Fixes gh-3877.
what_new entry for KD and BallTree doc fixes
Added feature to fix #1523
ENH decision_function now returns #votes and scaled scores.
TST Added test to assertain correlation of decision function and prediction
FIX Implemented _check_is_fitted for OvO similar to the one for OvR
FIX Correct and separate the scaling logic for scores
TST test_ovo_ties will now use decision_function to calc votes and scores