Show syntax for specifying multiple shorthand pairs

This is a frequent enough question that it makes sense to
document that multiple list values are specified as
``--arg a=b,c=d a=b,c=d`` vs. ``--arg a=b,c=d``.
Add missing test for list-structure(list-scalar, scalar) docs
Rename "--filter" to "--filters"

Technically accepted by python's argparse, but our examples
should use the documented argument name.
Merge branch 'better-shorthand-docs' into develop

* better-shorthand-docs:
  Add missing test for list-structure(list-scalar, scalar) docs
  Show syntax for specifying multiple shorthand pairs
Merge branch 'doc-example-cleanup' into develop

* doc-example-cleanup:
  Rename "--filter" to "--filters"