BUG don't densify sparse matrix in BernoulliRBM.score_samples

Also documented the non-determinism of this method.
ENH speed up progress reporting in RBM

Previously took up to 45% (!) of the time in training, not the 10% promised
in the docstring, for the digits example. Now down to at most 3%.

Pseudo-likelihood is now reported for the entire X, rather than batch-by-batch,
which will take more memory.
DOC fix BernoulliRBM._fit docstring

Return value is gone now. Thanks @jnothman.
Merge pull request #2642 from larsmans/rbm-speedup

[MRG] faster convergence reporting in RBMs
ENH: faster cartesian product in make_classification and document complexity

This version
* is 4-6x faster
* takes less memory, and
* (on my box) is more likely to give a decent MemoryError instead of
  triggering the OOM killer, because it allocates in one go.

See #2534.
Revert "ENH: faster cartesian product in make_classification and document complexity"

This reverts commit 03352bf5f96e01487fd7bdcb49fb8416cabcf6ea.

Apparently doesn't work with older NumPy.
Fix exception message when cloning a estimator that does not implement 'get_params' method.
Merge pull request #2647 from trein/patch-1

Fix exception message when cloning an estimator
Merge pull request #2643 from jnothman/bench_mutilabel_metrics

[MRG] Add benchmarking script for multilabel metrics
DOC: PolynomialFeatures narrative doc
DOC: fix auto-links
DOC: fix Polynomial Regression docs
ENH: Raise explicitly on non-unique vocab.
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