Gets a property of an object.
value must have been initialized to the expected type of the property (or a type to which the expected type can be transformed)
In general, a copy is made of the property contents and the caller is responsible for freeing the memory by calling unset.
Note that get_property is really intended for language bindings, @get is much more convenient for C programming.
the name of the property to get
return location for the property value