Capability to attach multiple "on_*" handlers

[walro]

I think that the current behavior is that the last setup on_* would "win".

For one it would make testing so much easier. See 56927d9#commitcomment-14448933 for some context.

[twingly-mob]

Another way (as we just discussed IRL) could be exposing @client.register_event_listener to the user, then the user could register an arbitrary number of handlers.

That is what mysql-binlog-connector does in its test: https://github.com/shyiko/mysql-binlog-connector-java/blob/0.2.4/src/test/java/com/github/shyiko/mysql/binlog/BinaryLogClientTest.java#L32-L44

We would need to expose SaveEventListener and RowEventListener so the user could use them as handlers, if the user thinks they are suitable.

[dentarg]

There was some back and forth about multiple listeners in shyiko/mysql-binlog-connector-java#15