DOC: Fixes for doc/source/user/basics.io.genfromtxt.rst.

Add missing part of usecols negative index explanation and other
minor redaction fixes.
MAINT: Cleanup doc/source/user/basics.io.genfromtxt.rst.

Remove trailing whitespace.
Break long lines.
Fix some indentation.
Use the `::` directive to indicate interactive examples.
ENH: inv/solve work with empty inner and others empty outer array

This makes the inverse of a 0x0 array simply be 0x0 again. It
also modifies the no-empty array check in favor of a no-empty
*inner* array, since the gufuncs seem to handle the other case
fine.
ENH: For smaller array, added macro NPY_BEGIN_THREADS_THRESHOLDED in ndarraytypes.h
Avoiding NPY_BEGIN_THREADS for small arrays, can speed-up trivial_three_operand_loop by 5%.
As releases of GIL, then quickly restoring just after small operation doesn't benefit.
Merge pull request #3521 from arinkverma/gsoc_performance

ENH: Avoiding NPY_BEGIN_THREADS for small arrays can speed-up trivial_three_operand_loop by 5%
Merge pull request #3565 from charris/documentation-fixes

Documentation fixes for `basics.io.genfromtxt.rst` and `creation.py`
Merge pull request #3513 from seberg/0d-linalg

ENH: inv/solve work with empty inner and others empty outer array
ENH: improve numpy.all()/any()

Unroll the loop once and use pminub/pmaxub to save a slow pmovmskb
instruction. Improves performance by 50% on some AMD chips.
Also add a pure libc path using memcmp and memchr for non amd64 systems.
The libc path can be faster with a very modern cpu and libc version,
e.g. an i7 with glibc 2.17 is about 20% faster than our code but many
other tested platforms are much slower (2.12 xeon, core2duo) or same
speed (2.17 phenom).
The numpy code can be removed in future when faster libc versions and
cpus are more commonly available.
MAINT: move npy_is_aligned to common.h

also make it and some other alignment operators a bit faster by using
unsigned integers and bitwise and if possible.
Make use of npy_is_aligned in _IsAligned too.
ENH: add NPY_LIKELY and NPY_UNLIKELY macros for branching hints

Use it for npy_is_aligned expecting alignments of the power of two.
Cuts down the time spent in _IsAligned by the testsuite relative
to the rest of multiarray.so from 0.6% to 0.4%
Fix documentation description of loop spam in interactive interpreter
MAINT: remove unused and broken parts of numpy.testing

Deprecate np.testing.importall - it's pointless and partially broken.
Merge pull request #3597 from rgommers/testing-module-cleanup

MAINT: remove unused and broken parts of numpy.testing
Merge pull request #3596 from ecprice/a

Fix documentation description of loop spam in interactive interpreter
Merge pull request #3517 from juliantaylor/memchr-all-any

ENH: use memchr for unit stride all/any
BUG: Fix PyType_FastSubclass() check for numpy.int_

Signed-off-by: Yury V. Zaytsev <yury@shurup.com>
BUG: Document that numpy.int_ doesn't inherit from int on Py3k

Signed-off-by: Yury V. Zaytsev <yury@shurup.com>
TST: Add regression test to check numpy.int_ inheritance on Py2/Py3

Signed-off-by: Yury V. Zaytsev <yury@shurup.com>
BUG: Fix test_operand_flags test.

The test tests an inner loop in operand_flag_tests.c.src that expects
a long type, but it is tested using 'i8'. This fails when long is not
'i8'.

Closes #3363.
Merge pull request #3526 from zyv/fix_int_inheritance

BUG: Fix PyType_FastSubclass() check for numpy.int_ and Py3k inheritance