Writer to ds

WriteImage method for DataSet (dataset.py)

Changes introduced:

• dataset.WriteImage method added to the DataSet class.

• GetAttenuation method added to the DataSet class.

• GetPhase method added to the DataSet class.

Have changed the name of dataset.WriteImage's argument prefix to proj_type. (Couldn't think of a good name)

The rest remains as before.

Just to be sure, it now looks like:

 def WriteImage(self, data, proj_type, projection_number, *args):

        if proj_type.lower() == 'phase':
            pref = self.phase_prefix
        elif proj_type.lower() == 'attenuation':
            pref =  self.retrieved_attenuation_prefix
        elif proj_type.lower() == 'phase update':
            pref = self.update_prefix
        elif proj_type.lower() == 'attenuation update':
            pref = self.attenuation_update_prefix
        elif proj_type.lower() == 'intensity':
            pref = self.propagated_prefix
               . . . 

Please let me know if I misunderstood your earlier comments!