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%
Merge pull request #3594 from juliantaylor/is_aligned_maint

MAINT: move npy_is_aligned to common.h