DOC: fixed correlate docstring.

Replaced correlation formula with corrected version that matches the
numpy implementation. Added comment on possible further different
definitions of correlation. Added examples.
DOC: replaced typeset formulas by pure ASCII equivalents.

Replaced typeset formulas by pure ASCII equivalents. Should now be
easier to read in source files.
MAINT: add NPY_CPU_HAVE_UNALIGNED_ACCESS macro

currently only i386 and amd64, must be used carefully as the compiler
may still be allowed to assume alignment and try to vectorize based on
type size alignment.
added spaces to literal string concats

literal string concatination without spaces not
allowed in C++11 anymore
BUG: fix declaration-after-statement

closes gh-3930
Merge pull request #3932 from juliantaylor/windows-annoyance

BUG: fix declaration-after-statement
Merge pull request #3929 from chrodan/strc++11

add spaces to literal string concatination for C++11 compatibility
MAINT: silence warning by casting to right type
MAINT: add npy_memchr for memchr like operations

useful for small sizes where the function call is expensive.
Merge pull request #3913 from bspinnler/fix_correlate_docstring

DOC: fixed correlate docstring.
ENH: improve npy_memchr(p, 0) by using __builtin_ctz (tzcnt on x86)

Improves sparse mask performance by about a factor of three, the worst
case of no consecutive mask elements slows down by about 10%-15%.
Merge pull request #3931 from juliantaylor/memchr-move

move memchr like code to a function