Allow configuration of pressed background color.
Don't assume every drawable passed in is a BitmapDrawable.
Properly recycle the TypedArray.
Convert shadow values to be dimensions.

That way they'll be automatically scaled to device density, and it's
easier to map them in mind to other sizes in XML.
Change FAB scaling algorithm.

Instead of growing the FAB together with the view with a fixed ratio,
introduce a 'radius' attribute defaulting to 28dp (as per Google's
guidelines) and measure the view in a way that accounts for both radius
and shadowRadius. The old way didn't work for unusual shadow sizes.