Can't serialize smarts query object (python)

As indigo uses ctypes objects containing pointers, can't be serialized using pickle.

Molecule objects can be easilly serialized with mol.serialize() method, but trying to serialize query object loaded from SMARTS generates and exception.
```
query = indigo.loadSmarts("c1nc(C)nc(O)c1")
query.serialize()

IndigoException: core: is not a molecule
```

It would be nice to be able to serialize them in order to use it with multiprocessing library.