DOC: tweak the stats tutorial

Remove a cautionary note which no longer applies.
DEP: stats: deprecate zprob, fprob, ksprob
BUG: sparse: fix int32 wraparounds in BSR matrices

The issue here is that the nnz of BSR is not bounded by the index data
type, which only bounds the number of blocks.  The block size may easily
overflow int32.
BUG: sparse: fix integer overflow in CSR matmat
TST: sparse: add tests probing for int32 overflows
MAINT: update scipy-sphinx-theme
Merge pull request #3239 from bmcage/monohermspline

DOC: interpolate: correct doc for pchip interpolation
Merge pull request #3241 from matthew-brett/relax-mio-write-check

BUG: io/matlab: check write attr of fileobject without writing
Avoid using np.take(x,x); use mode='clip'
DOC: document how to run slow tests
TST: sparse: add a benchmark for sparse __setitem__ and __getitem__
DOC: stats: mention deprecations in the release notes
BUG/ENH: stats: make frozen distributions separate instances

Previously, rv_frozen instances held a reference to a global distribution
instance.
MAINT: stats: use/mention stats.XXX.sf methods instead of special.YYY
ENH support CSR/CSC __setitem__ where duplicates interfere

Also use izip instead of zip
ENH much more efficient sparse min/max with axis
ENH function to return nnz per row/column in some sparse matrices
TST/FIX better test coverage for minmax, and handle 0-size
TST ndarray-compatible handling of zero-size arrays in max/min
ENH: added C sqeuclidean_distance, pdist_sqeuclidean and cdist_sqeuclidean