DOC more complete coverage of API linking in examples

Previously ignored non-plot files.

Avoids some link over/undergeneration
TST add test for name identification in RST generation
TST avoid nose running setup() in gen_rst.py
TST add sphinxext to testing
TST remove dependencies for testing sphinxext
DOC Note shape of binary binarized output
bug fix and deprectation warning added to cross-validation
COSMIT factor out split data as struct
Merge pull request #3165 from jnothman/links_in_examples

DOC more complete coverage of API linking in examples
Merge branch 'master' of https://github.com/scikit-learn/scikit-learn into bootstrap
Merge pull request #3295 from rphlypo/bootstrap_traintest

[MRG+1] exception in bootstrap must be evoked when n_train + n_test > n (resolves issue #3290)
DOC fix bad formatting in decomposition.rst
FIX python 3 compat for plot_bias_variance.py
FIX OvR with constant label for non-predict methods
DOC safer way to run the tests under windows
FIX case where label is constantly absent
MAINT: symeig->eigh
FIX Python 3 support for datasets.species_distributions
FIX ensure that matplotlib.use('Agg') is called first when building the docs
DOC formatting fixes in whats_new.rst