Support an existing 'events' function attribute

I occasionally define 'events' as a method on a view (instead of a hash):

```coffeescript
class SampleView extends Backbone.View

  events: ->
    click: -> alert 'Clicked!'
```

Backbone supports this but when I tried to use stickit to bind to a form field the field events were never added to 'events' because 'events' was a function and not a hash. This pull requests adds support for an 'events' function. I added tests for this new case as well as the 'events as hash' case.

Thank you for stickit - I'm looking forward to using it more and contributing where I can!