ENH: copy ndarrays if they are encountered in setArrayFromSequence

By avoiding the elementwise copy array([a,b,c]) is now as
fast as vstack([a,b,c])
BUG: PyArray_SelectkindConverter should be in conversion_utils.h.

Also include numpy/ndarraytypes.h, although this seems not needed in
practice.
Merge pull request #3709 from charris/update-conversion_utils_h

BUG: PyArray_SelectkindConverter should be in conversion_utils.h.
BUG: Fix 0-sized ndindex

The zerosize_ok flag to nditer was missing, so that it did not
allow for 0-sized iteration.

Closes gh-3714
Merge pull request #3696 from juliantaylor/copy-array-create

ENH: copy ndarrays if they are encountered in setArrayFromSequence
Merge pull request #3715 from seberg/ndindex-0size

BUG: Fix 0-sized ndindex