DEP: put back veccdf/vecfunc/vec_generic_momemt in stats.distributions.

Removed erroneously in gh-3243 for 0.14.0.  These methods were always
private ones but not marked as such, and as the comments on gh-3243 show
they were used. Hence now deprecated.
ENH: cluster: reimplement the update-step of K-means in Cython
MAINT: cluster: remove the conditional import for _vq
BUG: stub out spurious methods of Akima1DIntgerpolator

from_spline and from_bernstein_basis are inherited
from PPoly, and neither produces an Akima interpolator.
DOC: add See Also sections to Pchip and Akima interpolators
ENH: add multivariate normal option to return the effective rank
MAINT: remove return_rank optional argument, add .rank multivariate_normal_frozen attribute, add tests
MAINT: learn how to use frozen distributions
MAINT: aggregate covariance matrix info into an object
MAINT: do not silently reduce dimensionality, but allow reduction with a forcing flag
TST: more tests for singular covariance matrices
DOC: one eigh -> one call to eigh
DOC: add the allow_singular flag to more parts of the docs
MAINT: add mvn error checking
MAINT: typos
DOC: move __init__ docstring into the class docstring
Merge pull request #3141 from argriffing/mvn-return-rank

ENH: add multivariate normal option to return the effective rank
MAINT: reinstate symeig but with deprecation decorator
Merge pull request #3752 from argriffing/restore-deprecated-symeig

MAINT: reinstate symeig but with deprecation decorator
MAINT: avoid indexing with a float array