Custom hooks are not powerful enough and not unloaded

[rwstauner]

Behave offers hooks for custom keydown events but they are added too late to be able to override Behave functionality (and they offer no method to cancel the event).

So for example, if I want to intercept shift+enter to do my own thing, I can't stop Behave from editing the text without disabling the autoIndent feature altogether.

Additionally I noticed that listen adds 4 Behave events and 2 hook events, but destroy only removes the 4 Behave events (not the 2 hook events).