DOC: PolynomialFeatures narrative doc
DOC: fix auto-links
DOC: fix Polynomial Regression docs
remove EllipticEnvelop deprecation
Merge pull request #2653 from jaquesgrobler/remove_ellipticenvelope_deprecation

remove EllipticEnvelop deprecation
Remove deprecated zero_one and zero_one_score
Merge pull request #2649 from jakevdp/polynomial_doc

DOC: Polynomial regression narrative doc
flake8
Merge pull request #2654 from arjoly/metrics-0.15

[MRG] Remove deprecated zero_one and zero_one_score
DOC: fix test failure in linear model
Website: add spotify testimonials
Merge pull request #2651 from amueller/spotify_testimonial

MRG Website: add spotify testimonials