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.
fix numpy.i for python 3

PyFile_Check and PyInstance_Check have been removed from the C API
for python 3.  This removes calls to those two functions from
numpy.i for PY_MAJOR_VERSION >= 3 so that it builds with a
python 3 Python.h.
BUG: Fix segfault in np.result_type for None input.

Makes behavior identical to np.dtype(None), which fits to how
the function works.
Merge pull request #2933 from seberg/result_type-segfault

BUG: Fix segfault in np.result_type for None input.
BUG: gh-2935, fix printing of scalar float -0.0.

The issue was that the string value of scalar floating types equal to -0.0
lacked a trailing ".0".

    >>> print np.float64(-0.0)
    -0

The problem resulted from using val < 0 to check for a leading negative
sign. That expression evaluates false when val = -0.0, and the need to
append ".0" was not detected.
TST: Add test for printing of scalar values.
Merge pull request #2936 from charris/fix-print-negative-float-zero

Fix print negative float zero
Merge pull request #2923 from baeuml/swig-fix-python3

fix numpy.i for python 3
BUG: fix inclusion of private hader in #d2122ea1f458e9429b692111238f7b9f4a852db2
BUG: fix separate compilation mode for bento build.
Fix-up logic for checking for zero-d arrays.
TST: Add a test for ndindex call.
Merge pull request #2725 from seberg/take_0d

ENH: Allow 0-d indexes in np.take
Merge pull request #2940 from ContinuumIO/ndindex_fix_more

BUG: Fix logic in ndindex to match __init__ method.   Fixes bug in ndindex((3,))
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.