Docstring: point to correct equivalent function

np.compress' "See also" pointed to itself instead to equivalent np.extract
BUG: linalg: norm was computing and then ignoring a product
MAINT: linalg: some more clean up in norm: 'nd' was defined but not used
Merge pull request #3539 from WarrenWeckesser/bug-norm-performance

BUG: linalg: norm was computing and then ignoring a product
Update halffloat.c

Corrected preprocessor form.
Repaired my misunderstanding and added np.extract

I overlooked that np.compress and ndarray.compress are different things and wrongly assumed that it was a typo. I corrected that and added np.extract for equivalency for 1-D arrays.
Merge pull request #3538 from michaelaye/patch-1

Docstring: point to correct equivalent function (one word change)
Link cumsum and diff to one another as theyre roughly the inverse of each other
Merge pull request #3546 from nils-werner/cumsum-diff-link

Link cumsum and diff to one another...
Merge pull request #3541 from jeromekelleher/patch-1

BUG: make preprocessor tests consistent in halffloat.c
DOC: use the new scipy-sphinx-theme in the documentation
DOC: update scipy.org doc build Makefile targets
MAINT: ensure the sphinx theme gets included in source tarballs
DOC: put release notes in inverse order
DOC:Some minor proofreading of Tests introduction
Merge pull request #3549 from pv/doc-theme

DOC: use the new scipy-sphinx-theme in the documentation
Move numpydoc to a separate repository
Add Numpydoc as a git submodule
DOC: fix HOWTO_BUILD_DOCS.rst.txt
Merge pull request #3547 from pv/numpydoc-move

Numpydoc move