Return boolean & prefix for prefixed properties

[lukeed]

3Dtransforms, transforms, and transitions are fetching the vendor-prefixed value anyway... might as well tell the end-user what Feature.js found.

With this change, those 3 features will return an Object of

{
  support: Boolean, 
  property: String || null
}

For the sake of brevity / bytes, these keys could be renamed to use and prop.