DOC fix formatting of attributes etc. in docstrings
DOC move Attributes section to after Parameters and style likewise
MAINT use assert_warns
MAINT Fix regression random projections work sparse matrices
DOC whats_new.rst: missing backported fixes for 0.15.1
fix: i might be undefined
FIX six issue with module imports

Fixes #3518, #3519.

Inspired by Johannes Schönberger's patch to scikit-image,
https://github.com/scikit-image/scikit-image/commit/71743d2d6ff3666c9530278dfd650c2435fa15d9
Max iter param in Liblinear is now softcoded
ENH: Return n_iter_ from liblinear and print convergence warnings
TST: Added test to check ConvergenceWarning
Update plot_tree_regression.py

Import statements have been moved to the beginning of the file.
Merge pull request #3522 from ugurthemaster/patch-1

Update plot_tree_regression.py
FIX #3485: class_weight='auto' on SGDClassifier
FIX wording in whats new in 0.15.1
Merge pull request #3509 from arjoly/fix-rp-sparse

[MRG] MAINT regression: random projection should work with sparse matrix
Merge pull request #3489 from jnothman/attributes-doc

[MRG] DOC fix formatting of Attributes sections in documentation
DOC remove backticks from around attribute name + PEP8
ENH faster, low-memory PolynomialFeatures
FIX ensure output and input have same dtype