Schema option callback="(class::)method" added to xPDOObject::set()

Modified xPDOObject::set() to read map for generated="callback" and callback="(class::)method". And check if callable and sets for call to call_user_func_array

&lt;object generated="callback" callback="MyClass::StaticMethod" />
and
&lt;object generated="callback" callback="myFunc" /> Both work. 


Have not added tests to unit testing