Update to mean shit clustering narrative documentation.
Update to docstring of meanshift
docstring of module
Fix typos found by Alexandre
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
Merge pull request #2768 from robertlayton/meanshiftdoc

MRG: Update to Mean Shift clustering documentation
Minor doc example fix