Extend PyRDF.initialize to "string code" and functions from imported modules

[JavierCVilla]

Currently PyRDF.include only supports python callable of this shape:

def f(a, b, c):
     import ROOT
     ROOT.myCppFunction(a, b, c)

PyRDF.initialize(f, a, b, c)

It would be useful to support any of the following calls:

PyRDF.initialize(ROOT.myCppFunction, a, b, c)
PyRDF.initialize("myCppFunction", a, b, c)
PyRDF.initialize(f, a, b, c) 

This way the code would be cleaner.

[vepadulano]

This could be refactored with the new PyROOT feature to wrap any python function in a C++ function pointer and execute it on the C++ side. To be seen