Issue #23: Make agentx.py module executable for testing.
Issue #23: Move library definitions to the beginning of the module.
Issue #23: Add generic and Counter64-specific get_value() methods.
Issue #23: Explicitely specify library return types even if int (default).
Issue #23: Document unused pointer members.
Issue #23: Split handler registration creation into its own method.
Issue #23: Update example agent with latest register_value() changes and demonstrate changing values.
Issue #23: Add table support to custom agentx module.