Remove vectorized form and property API

[non-Jedi]

Since any function call can now be called in a "vectorized" form using broadcast syntax, the vectorized form and property methods should now be deprecated for the sake of maintainability. In some scenarios, the broadcasted form should perform better than the current vectorized form due to automatic broadcast fusion. Obviously, this is a breaking change, and many call sites in Gadfly would need to be updated simultaneously with this change.

[Mattriks]

Note that Compose's vectorised form produces a Compose.Form{<:Compose.FormPrimitive}. Broadcasting a form e.g. ellipse.([0.5], [0.5], [0.1,0.2,0.3], [0.3,0.2,0.1]) produces an Array of forms, which is not the same thing.

Also see #163, which was a previous attempt.