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 memory leak in ndarray construction from strings (gh-2927)
Merge pull request #2928 from mwiebe/string_init_memleak

BUG: Fix memory leak in ndarray construction from strings (gh-2927)
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.
Merge pull request #2725 from seberg/take_0d

ENH: Allow 0-d indexes in np.take
ENH: Add safe step argument to linspace

This adds a step argument to linspace, however the step argument is only
used to determine the integer number of steps. It must be possible to safely
determine the number of steps (given floating point accuracy).

This was requested in gh-630.
BUG: preserve datatype in linspace corner-cases

The linspace corner cases always returned float, but the rest of the
function did support complex or high precision floating point numbers.