Significant cleanup x 11.

This commit is the next in a commit chain quietly resurrecting BETSE
for a modern audience and the modern Python ecosystem. Specifically,
this commit begins resolving failing GitHub Actions-based continuous
integration (CI) workflows. BETSE 1.4.0 is now still days from official
release, supposedly. (*Hog the bog!*)

.github/workflows/python_test.yml

@@ -104,7 +104,6 @@ jobs:
         # the "[tox]" subsection in "tox.ini") to be tested, which the
         # ${TOXENV} environment variable declared below exposes to "tox".
         tox-env:
-          - py39-coverage
           - py310-coverage
           - py311-coverage
           - py312-coverage

betse/util/py/module/pymodname.py

@@ -39,7 +39,9 @@
     initial_mapping={
         'Numpy':  'numpy',
         'Pillow': 'PIL',
+        'pillow': 'PIL',
         'PyYAML': 'yaml',
+        'pyyaml': 'yaml',
         'SciPy':  'scipy',
     }
 )