Have sphinx > 3.0 ignore monkeypatched sas.models

sas.models is a monkeypatched sasmodels that breaks sphinx autodoc.

Fixing this in a way that is compatible with both sphinx 1.8 and 3.x seems
difficult, so put a sphinx version check on the fix.

See SasView#1744

docs/sphinx-docs/source/conf.py

@@ -313,3 +313,15 @@
         rst_prolog = fid.read()
 
 numfig = True
+
+import sphinx
+if sphinx.version_info[0] >= 3:   # CRUFT
+
+    # Skip the monkey-patched 'sas.models' which grafts the sasmodels classes
+    # back into their old location in sasview, but causes autodoc to explode.
+    def autodoc_skip_member_handler(app, what, name, obj, skip, options):
+        return name.startswith("sas.models")
+
+    def setup(app):
+        # Connect the autodoc-skip-member event from apidoc to the callback
+        app.connect('autodoc-skip-member', autodoc_skip_member_handler)