MAINT: Update links to numpydoc source code and README

These links pointed to numpydoc's location within the numpy project on Github, but it has since been split out to a separate repository, breaking the links.
Merge pull request #4055 from takluyver/patch-2

MAINT: Update links to numpydoc source code and README
DOC: use variable names in formula for convolve

Use the variables names `a` and `v` as used in the function instead of
using `f` and `g`. This makes it clearer which array "slides" along the other.
Fix typo.
Merge pull request #4047 from arunpersaud/convolve_doc

DOC: use variable names in formula for convolve
Merge pull request #4056 from herr-biber/master

Fix typo.
Merge pull request #4020 from juliantaylor/memcrash

BUG: fix missing check for memory allocation failure in ufuncs
MAINT: make NPY_CPU_HAVE_UNALIGNED_ACCESS a numeric macro

allows using it in if statements like for count_nonzero
also fix a compiler warning by casting
Merge pull request #4057 from juliantaylor/unaligned-macro

MAINT: make NPY_CPU_HAVE_UNALIGNED_ACCESS a numeric macro
ENH: improve add_newdocs performance

replace slow exec with a direct __import__.
improves `import numpy` speed by about 10%.
Merge pull request #3980 from larsmans/refactor-gemm-gemv

MAINT: dotblas: factor out all gemm and gemv calls
DOC: Improved doc for boolean array indexing
Merge pull request #4064 from juliantaylor/import-speed

ENH: improve add_newdocs performance
BUG/ENH: blasdot: make *dot calls 64-bit safe

BLAS uses int for all its size types, so the size is going to be
silently truncated on platforms where sizeof npy_intp > sizeof int,
i.e. on modern 64-bit platforms. In this case, we do a dot product
in reasonably-sized chunks and add the result ourselves.

On platforms where sizeof(int) == sizeof(npy_intp), i.e. typical
32-bit platforms, it's up to the compiler to optimize the loop away.

Also tried to make the code more readable, replaced int by npy_intp
in a few places and removed useless register declarations (modern
compilers ignore those).
ENH: dotblas: re-route all cblas_?dot calls to chunked versions

Also factored out and simplified NumPy->BLAS stride conversion.
ENH: Use nditer in numpy.save to stream bytes to custom file objects
TST: Increase test coverage of numpy.save/load roundtrips
Merge pull request #4077 from ogrisel/streaming-numpy-save

Streaming numpy.save to arbitrary file objects
ENH: intern some commonly used strings in umath module

Allows using the PyObject dictionary functions instead of the costly
C-string variants.

Make use of this in some of the ufunc subtype wrapper functions.

Improvement:

    a, b = np.arange(200.), np.arange(200.)
    %timeit np.add(a, b, out=a)
    1000000 loops, best of 3: 768 ns per loop

vs before:

    %timeit np.add(a, b, out=a)
    1000000 loops, best of 3: 1.03 µs per loop
ENH: skip redundant checking of subok keyword in _find_array_prepare

all currently existing callers only call this function if subok has
already been checked to be true, but keep the code to make clear it has
to be checked.