FIX PLSRegression again supports 1d target

Fixes plot_compare_cross_decomposition example
FIX clip SGD gradient on linear models for stability

The l2 weight decay rescaling is also kept positive (or null)
in case of strong regularization.
WEB fix css for new version of sphinx.
Use plot_galler=0 in makefile for sphinx >1.2.3 Also works with 1.2.3
MAINT refactor gradient boosting code

Fixes gh-3790
TST update numerical overflow (non-regression) tests
Fixes #3644
Added NRT for return_path propagation check
DOC: Fix LabelBinarizer docstring to rst format bug

- Also add line to make multilabel classification example more instructive
- Use one line for 2D array so syntax highlighting is correct
Merge pull request #3883 from ogrisel/sgd-stability

Improve stability of SGDClassifier / SGDRegressor with gradient clipping
DOC update whats_new.rst for SGD stability
FIX unlikely pickling error of splitters
TST add a toy test for min_weight_samples_leaf
Merge pull request #3823 from ragv/omp-3644

[MRG+1] Fixes #3644
Typo
Update plot_outlier_detection.py

I think this word should be inliers.
Merge pull request #3889 from jdcaballero/master

Update plot_outlier_detection.py
DOC: COSMIT: Naive Bayes long url + PEP8 cleanup

* Put long link to IR-book on its own line to make sure it renders as a
  correct link in the docs.

* Put long ValueError messages that were breaking PEP8 compliance of
  the file `naive_bayes.py` into temporary variables.

Signed-off-by: mr.Shu <mr@shu.io>
Merge pull request #3892 from mrshu/mrshu/naive-bayes-small-fixes

DOC: COSMIT: Naive Bayes long url + PEP8 cleanup
DOC narrative docs for grid search's robustness to failure