Maintaining a map of bound handlers in yet another data structure isn’t nice. Since it’s uncommon to unbind particular handlers, we don’t need to make that task easy IMHO.

`@delegate` already returns the bound handler so one can store it for unbinding:
```
# Doesn’ work:
@delegate 'click', @handler
@undelegate 'click', @handler
# Works:
boundHandler = @delegate 'click', @handler
@undelegate 'click', boundHandler
```