BUG: Fix reference leak in PyArray_IntpFromIndexSequence.

This caused {ones, zeros, empty}([1]*10) to increase the reference
count of 1 by 10. Same for other numbers in the list.

Closes #3589.
TST: Add test for reference leak in zeros, ones, empty, and full.

Check that the reference counts of the  passed dimensions do not
change.
MAINT: Remove some commented out code in test_indexing.py.

The code was intended to check refcounting, and indeed, exposed a long
standing bug by failing, which is why it was commented out. That bug is
now fixed and tested by gh-3631, so the commented out code could
theoretically be made to work, but that requires enough del this and del
the other that I think it is too fragile to keep. So delete it.
Merge pull request #3632 from charris/remove-commented-out-code

MAINT: Remove some commented out code in test_indexing.py.
Merge pull request #3631 from charris/fix-reference-leak

Fix reference leak
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