Proposed 'short' release notes:

REL: v2.2.4 LTS

The forth bug-fix release of the v2.2 LTS series.

• Fix a memory leak with PySide2
• rename :math: sphinx directive to :mathmpl: to work with sphinx >
  1.8. Both versions are now available if sphinx < 1.8
• avoids numpy deprecation warnings
• fixes to tests to work with pytest >= 3.8 and the minimum is now pytest >= 3.6

jquery-ui is no longer bundled in git repo and is downloaded during
the install or sdist process. If you are installing from pypi the
files will be included, but if you are installing from git you will
need internet access the first time you run pip install .. The
install process tries to cache the files and will not need internet
access on future installations.

fixes to tests to work with pytest >= 3.8

Minimum supported version was also bumped to 3.6.