Don't send WONT in response to DO/DONT if an event listener is present.
If the client sends a DO or DONT command, wez-telnet automatically responds with WONT. Now, if an event listener 'do' or 'dont' is present, the automatic response is skipped so that the application can customize the response.

Export all the command and options constants so that application code can access them. Export them at top-level so that they can be referred to concisely from application code.