BUG: sparse: smarter random index selection

Fixes gh-3648.
Merge pull request #3650 from perimosocordiae/patch-5

BUG: sparse: smarter random index selection
ENH: cluster: rewrite and optimized `vq` in Cython

Rewrite the underlying part of cluster.vq in Cython.
Besides, an optimized algorithm is implemented and it will improve the
performance for datasets with large nfeat when built with an optimized
BLAS library.
BLD: Bento build scripts for new cluster._vq
MAINT: cluster: rewrite vq with fused types and BLAS Fortran ABI
MAINT: cluster: avoid copying when dtype is the same in vq
Merge pull request #3683 from richardtsai/vq_rewrite

ENH: cluster: rewrite and optimize `vq` in Cython
Update continuous.rst

fixes #3587
Merge pull request #3695 from andreas-h/patch-3

DOC: update continuous.rst so distributions are in alphabetic order.
ENH: check for valid 'orientation' kwarg in dendrogram()

fixes #3668
Merge pull request #3696 from andreas-h/gh3668

ENH: check for valid 'orientation' kwarg in dendrogram()
ENH: Implement faster multivariate integration in scipy.integrate.

The numerical integration routines in SciPy use a well-tested, fast, Fortran
library. The computational cost of integration with these routines can be
greatly reduced if the function to be integrated is compiled and passed to
the library directly, avoiding callbacks to the Python interpreter.
TST: Preliminary implementation of unit tests for faster integration.
TST: Cross-platform build and install of unit tests.
DOC: Updated THANKS.txt and scipy 0.15.0 release notes.
TST: fix mistake in release notes