adding example for memory wrapper
A short cleanup
Merge pull request #3795 from dsullivan7/svm_doc

[MRG+1] adding example for memory wrapper for load_svm_light
recovering deleted variable
MAINT remove deprecated loss in gradient boosting
Handle_unknown option to OneHotEncoder

OneHotEncoder fails with a error that is not helpful if a missing
categorical feature is present during transformation.
Add handle_unknown with an "error" and an "ignore" option.
DOC add missing public function into the references
DOC: Remove extra # from url in fit.

The extra # messes with the rst parser which produces an invalid URL where the ".html" suffix is missing.
Merge pull request #3797 from Titan-C/clean

A short cleanup
Merge pull request #3801 from cmd-ntrf/typo_vbgmm

DOC: Remove extra # from url in fit.
DOC: Make the comment slightly clearer
Merge pull request #3800 from MechCoder/unknown_transform

Handle_unknown option to OneHotEncoder