Consider having a type parameter for CFArrays

[jrmuizel]

CFArrays can contain what ever you want to put in them, one just needs to supply an appropriate set of callbacks (CFArrayCallbacks) for working with them. For example, it would be valuable to be able to cast a CFArray<*c_void> to a CFArray<CFTypeRef> or even a CFArray<CFDictionary>. Unfortunately, there doesn't seem to be anyway to typecheck what is inside a CFArray so the casting would need to be unsafe.

[jrmuizel]

#127 implements this.

[jrmuizel]

This is fixed now.