Add prototype for validation curve
Add documentation and tests
Improve test coverage

... to 99%
Improve interface and documentation
Mocks inherit from BaseEstimator
Correct docstring
Add narrative documentation
Improve documentation

* add images
* add link to API doc
* change order
Fix link to validation curve
Add example with polynomial regression
Correct and improve documentation
Improve phrasing
Rephrase sentence
Simplify first part of the documentation
Fixed FS1995 citation.
Merge pull request #2825 from bryan-lunt/master

Fixed FS1995 citation.
MISC plot_rfe_with_cross_validation: better comments

Fixes #2817
Fix typo
Return scores of all folds

It is possible to plot confidence intervals with fill_between
DOC: grammar and spelling fixes