make IsotonicRegression pickleable
import pickle
fix svm.fit in feature_stacker.py
Merge pull request #3669 from pprett/fix-isotonic-pickling

[MRG+1] Make IsotonicRegression pickleable
ENH: Added median_absolute_error to metrics
DOC: Added doc in model_evaluation.rst
ENH: unit tests for median_absolute_error
Merge pull request #3742 from abhishekkrthakur/master

FIX remove svm.fit in feature_stacker.py
ENH: test_common.py unit tests pass
FIX: Small typo
Merge branch 'master' into median_absolute_error

Conflicts:
	doc/modules/model_evaluation.rst
DOC fix (Nu)SVR attribute shapes in docstring

Fixes #3673. Shapes were probably copy-pasted from (Nu)SVC.
XXX the attributes actually have strange shapes...
FIX sign flip in (Nu)SVR with linear kernel

Fixes #2933.
TST make catch_warnings blocks more robust
Merge pull request #3761 from FlorianWilhelm/median_absolute_error

add median absolute error (MAE) regression metric