Moved the partial
Added option for updating keypath on ractive with current width
Removed unused classes

resize-overflow and resize-underflow where never actually used for
anything..
Ractive allready has getComputedStyle polyfill
The decorator now auto-adds the required css

Also, classname for the resize sensor is now configurable through
Ractive.decorators.sensorClass.
Thanks @Rich_Harris for the suggestions.
Refactored out the CSS style creation
Updated the demo to reflect the changes caused by #1