ENH: Allow 0-d indexes in np.take

The TakeFrom already supported this. This removes the check which
made it not possible and adds some tests for take.

Also add documentation and information to the release notes.
BUG: Fix generalized ufunc so repeating labels in one input/output is ok
BUG: Missed case of broadcasting onto core dimensions in gufunc
BUG: Make sure the nditer doesn't complain when 0 broadcast dims
TST: Add test for gufunc scalar case
BUG: Fix bug in gufunc scalar case
TST: Test for a generalized ufunc bug, for zero-sized inputs
BUG: Fix for generalized ufunc zero-sized input case
compile fix on linux/mac
Fix-up logic for checking for zero-d arrays.
TST: Add a test for ndindex call.
BUG: npy-pkg-config ini files were missing after Bento build.
Merge pull request #2725 from seberg/take_0d

ENH: Allow 0-d indexes in np.take
BUG: gh-2790, fix column scaling in polynomial package least squares.

The columns should be scaled using their 2-norm, but in the complex case
that was being incorrectly computed as the square root of the sum of the
squared elements rather than as the square root of the  sum of their squared
real and imaginary parts.
TST: Add Test for column scaling in the polynomial package fits.

The test uses the complex set of sample points [1, 1j, -1, -1j] whose
squared sum is exactly zero. This would fail before the column scaling
was fixed.
Merge pull request #2940 from ContinuumIO/ndindex_fix_more

BUG: Fix logic in ndindex to match __init__ method.   Fixes bug in ndindex((3,))
MAINT: Use a better method to detect complex arrays.

Instead of

    if lhs.dtype.char in np.typecodes['Complex']:

use

    if issubclass(lhs.dtype.type, np.complexfloating):
REF: make the separate compilation env handling a tad simpler.
FEAT: use separate build by default.
DOC: mention the change of default for separate compilation.