Refactoring connection.

- Add config header with shorter name for freeflow namespace.
- Propagate ff namespace throughout.
Put everything in the nocontrol namespace.
Refactoring registry and acceptor.

- Moved registry into handler module.
- Require registration, deregestration to call open and close,
  thus simplifying the lifetime of handler users.
- Move acceptor into its own module.
Maintain all resource sets in the registry.

- Add Select_set to freeflow.
- Use the select set to maintain wait and dispatch lists.
- Automatically wait on read when adding a handler.