Scroller fix

fixes #1012, closes #1013

Contrary to the documentation, Scroller Class crashes if `window` is passed to the Class.

Docs were giving example with `window` as element. That breaks the code
as described in #1012

This PR changes the example in the docs to something one can copy/paste and see
it working "out of the box":  http://jsfiddle.net/v4yJD/

It changes also the first parameter info, from _element_ to _mixed_, since
code source uses `this.element = document.id(element);`

The source code fix was discussed in #1012, and is included in this PR.