Dispatcher pattern

[Gribouillis]

Uploaded version 2023.08.07.2 because

1. The dispatcher can point to other values than functions
   
2. The tables returned by dispatcher.__get__() now inherit collections.abc.MutableMapping with less code.
   
3. Code is amazingly short for what it does, a success for Python standard library's tools.
   
4. Interface is better than in previous versions.