.collect() for collecting responses from event handlers

This can be useful when using EventEmitter2 as a service locator where a component agnostically collects services/data from an unknown number of service/data providers.

For instance:

```
var results = emitter.collect("plugin", { profile: "default" });
```
`results` is an Array that contains a list of plugins (plugin event listeners that return plugin instances) that match the "default" profile.