Merge pull request #3157 from mjbommar/isotonic-increasing-auto

[MRG] Determine IsotonicRegression ``increasing`` by Pearson or Spearman corr rho
Explicitly invoke the Python interpreter.
Use double backticks.
Remove extraneous period.
Explain the -1 Python syntax.
Additional docstring fixes for issue #3167
Merge pull request #3197 from mjbommar/issue-3167-eradicate-todense

Additional fixes for .todense() / issue #3167
Merge branch 'master' of https://github.com/scikit-learn/scikit-learn
Adding tests to handle out_of_bounds parameter.
Adding out_of_bounds parameter to handle values outside training domain
Update plot_adaboost_regression.py

Library imports have been moved to top of the file.
Merge pull request #3200 from ugurthemaster/patch-2

Update plot_adaboost_regression.py
ENH: PEP257 style + small code simplication
Adding test for out_of_bounds argument validation
ENH: more explicit failure messages in test_common
Reworking .transform conditionals for out_of_bounds argument
PEP8 fix
Merge pull request #3199 from mjbommar/isotonic-out-of-bounds-2

Handling out-of-bounds in IsotonicRegression (clean PR #3147)
Merge pull request #3198 from apw/patch-1

Clarify shell versus Python syntax in tutorial.
Improved documentation of the "estimator_params" argument for RFE and RFECV.

Changed the documentation for the "estimator_params" argument for both
RFE and RFECV to better indicate how it could be useful for doing a
grid search. Previously the documentation may have indicated that RFE
and RFECV would perform a grid search if "estimator_params" was passed
a grid of parameter values, which is not the actual behavior.