Add quantile strategy to DummyRegressor. Fixes #3421.
Update what's new
Expose positive option in elasticnet and lasso path
COSMIT reshape for all regression strategy + avoid xrange
COSMIT  less nested constant check + use comprehension
Revert unwanted modificatoin
TST: Add tests and document whats_new.rst
Merge pull request #3778 from MechCoder/expose_positive

[MRG] Expose positive option in elasticnet and lasso path
DOC: FAQ: what to do with strings
Update what's new: full name of Staple