"cast-shadows" should map to "castShadows", not "castshadows" or "castShadows"

[hmans]

What we're doing today:

An attribute named castshadows will result in setting the castShadows property on the object wrapped by the element (since applyProps is currently scanning lower-cased property names as a fallback.)

Hyphens are currently interpreted to "enter" an object, ie. an attribute of foo-bar would set object.foo.bar.

What we should be doing:

• cast-shadows should set object.castShadows
• foo:bar should set object.foo.bar