Using showing without automatic triggering

I would like to integrate shower in another library, but to do that I need to trigger it manually for elements. My usage would be something like this:

```javascript
var slideshows = [];
// Build list of elements and do some DOM transforms
..
// Enable shower on the found slideshows
slideshows.every(shower);
```

Currently this is not possible because automatically runs for everything `.slide` and has no way to disable that or to manually trigger for another element.