ENH remove _is_1d and _check_1d_array thanks to @GaelVaroquaux
flake8
ENH raise ValueError with row vector if multilabel or multioutput is not supported
ENH being less permissive thanks to @jnothman
DOC add example is_multilabel
ENH handle properly row vector
Flake8
ENH better error message
FIX switch to the new format syntax
ENH prettier error message for _binary_clf_curve with bad input shape
ENH use ravel instead of atleast_1d and squeeze whenever possible
ENH coherently input checking for regression metrics
ENH dryer thanks to @jnothman
TST stronger test for _column_or_1d function
Cosmit
TST use TruncatedSVD in random forest tests

RandomizedPCA sparse matrix support is deprecated (and was only doing
an SVD anyway).
Merge branch 'pr_2002'
COSMIT refactor random forests

Very little subclass-specific stuff left in base classes.

Also fix faulty import in forest tests.
COSMIT refactor forests, part 2

Decouple RandomTreesEmbedding from ForestRegressor.