BUG: Fix PyBUF_SIMPLE flag to GetBuffer.

When no strides are requested, the array must be C-contiguous,
not only if a shape was also requested.

Closes gh-3613
DOC: Update 1.8.0-notes.rst

Note that the numpydoc sphinx extensions now reside in their own
repository.
Merge pull request #3616 from seberg/buffer-pybuf_simple

BUG: Fix PyBUF_SIMPLE flag to GetBuffer.
Merge pull request #3633 from charris/update-release-notes

DOC: Update 1.8.0-notes.rst