* Update developer requirements

* Run linter

* Fix links, use DOI links, wayback machine where required

* Add nx-guides to intersphinx mapping.

* Replace external mpl link w/ intersphinx.

* Update mpl intersphinx mapping.

Co-authored-by: Ross Barnowski <rossbar@berkeley.edu>

find -name "*py" | xargs grep -n '" % '
find -name "*py" | xargs grep -n '"\.format('
find -name "*py" | xargs grep -n "' %"
find -name "*py" | xargs grep -n 'msg % '
find -name "*py" | xargs grep -n ' %d '
find -name "*py" | xargs grep -n '\.format('

The copyright and author stuff is not necessary, out-of-date,
and inconsistent.  It takes up visual space and is a pain to
police everyone doing the same thing on the top of the module.

Git handles authorship in a comprehensive and authoritative way.
The LICENSE.txt file applies to all project code.