Major improvements, deduplication and simplification in over.app.

- over.app.ConfigFile can create empty config files and read all options from them
- over.callback was created to hold commandline parser callbacks
- over.app.Option.is_boolean hint added
- major improvements and increased robustness of over.app.Main command line parser

over/__init__.py

@@ -5,6 +5,7 @@ import sys
 
 from . import app
 from . import aux
+from . import callback
 from . import cmd
 from . import docs
 from . import file