Add returning reference support

[andot]

The old implementation of PHP-CPP do not support returning reference, but now it can.

for example:

myNamespace.add("myFunction", myFunction, {}, true);
myClass.method("myMethod", myMethod, {}, true);

Notice: Maybe this patch only works after patching #114.

[RogerWaters]

Hi,
is there any progress of this? It would be really nice if returning reference feature is available. Can you tell me if I can implement the magic function get like "public function &__get" with php-cpp?
Thanks for the nice wrapper.
RogerWaters

@andot tried your branch "returningref" and "master" but did not get returning reference feature to work. Is this because #114 ?