ENH: Allow ravel to reshape in place when possible

This fixes a lot of corner cases in reshape 'K' when the array
is not contiguous in the first place, it was previously never
ravelled in place.

Closes gh-5033
DOC: update numpy.extract docstring
Merge pull request #5075 from grlee77/docfix

DOC: update numpy.extract docstring
BUG: Readd the cblas.h header.

Rename cblas.h to npy_cblas.h and put it in numpy/core/src/private.
Fix the various includes to account for the change.

It turns out that MKL provides cblas, but not cblas.h. Rather, they
provide mkl_cblas.h, which also uses typedefs for the CBLAS_XXX enums.
Merge pull request #5078 from charris/add-back-cblas.h

BUG: Readd the cblas.h header.
Merge pull request #5034 from seberg/inplace-ravel

ENH: Allow ravel to reshape in place when possible