Readme can't work

[Strnadj]

Method process_event is in parent class without attributes. Always we can override method perform_handler, but it's useless, because if we do this, we are able only to use event perform... Last thing, if we override process_event, we have to write into body shutdown and exception handler. It will be nice to have in default switch clause perform_handler call instead of throwing an exception.

I am able to provide PR with previously mentioned behaviour.

[chadrem]

@Strnadj I've made some changes based on your feedback:

• README The Workers class advanced example should now work.
• You can now add custom events by overriding event_handler(event) and calling super(event) if you want the default handlers to work.
• Any event handler can now stop the event loop by setting @run = false

I believe these changes address all of your feedback. If not, please let me know.