MAINT: move byteswap macros to inlines in header

removes some duplication and allows older gcc that can't detect the
byteswap pattern to use the faster swapping instructions.
BUG: check alignment before loading the data

some cpus don't support loads that are not aligned to the elementsize.
regression introduced in 99cb95f7379a9.
MAINT: use npy_is_aligned in a few more places
Merge pull request #3376 from juliantaylor/unaligned-access

Unaligned access
DOC: fix a word in HOWTO_DOCUMENT.rst.txt.
Merge pull request #3383 from WarrenWeckesser/howto-doc-wording

DOC: fix a word in HOWTO_DOCUMENT.rst.txt.
BUG: fix memory leak and double execution in dot

introduced in 1.8.0dev 914294a42a
closes gh-3384
Merge pull request #3385 from juliantaylor/memleak-3384

BUG: fix memory leak and double execution in dot
ENH: linalg: Add the `axis` keyword to linalg.norm.

Also fixed a bug that occurred with integer arrays and negative ord.  For example,
norm([1, 3], -1) returned 1.0, but the correct value is 0.75.
MAINT: linalg: removed unused imports from linalg.py
DOC: linalg: Improve the docstring of the new norm function.
BUG: fix typo on npy_config.h include guard

Was overlooked as loops.c.src where np.isnan lives includes it directly.
Now all isnan calls in numpy profit from the improvement.
Merge pull request #3394 from juliantaylor/incl-guard-fix

BUG: fix typo on npy_config.h include guard
DOC: add to HOWTO_RELEASE to check that the benchmark suite runs.
DOC: Clarify and add C-compatible integer types to list of dtypes

Also mention np.intp, which at least personally I think is not an
unimportant type.
ENH: linalg: allow the 'axis' argument of linalg.norm to be a 2-tuple, in which case matrix norms of the collection of 2-D matrices are computed.
STY: linalg: some PEP8 clean up.
TST: linalg: loosen the requirements of some tests in test_blasdot.py.  Addresses part of gh-3399.
DOC: remove module index from reference guide.

It was broken, and after fixing it looked quite useless.
Update in conf.py is because `html_use_modindex` is deprecated.
DOC: add missing release notes to the reference guide.