Loaded data is not pickle-able by default

The namedtuple magic is preventing pickling of the data structures:

>>> f = File("src/protozfits/tests/resources/example_10evts.fits.fz")
>>> e = f.Events[0]
>>> pickle.dumps(e)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
_pickle.PicklingError: Can't pickle <class 'protozfits.CameraEvent'>: attribute lookup CameraEvent on protozfits failed