Initialise an API message from a transmission-safe dictionary.

def from_dict(self, d):
        """
        Initialise an API message from a transmission-safe dictionary.
        """
        for key in d:
            if key == 'data':
                for dkey in d['data']:
                    if dkey in self._encode_fields:
                        setattr(self, str(dkey), base64.b64decode(d['data'][dkey]))
                    else:
                        setattr(self, str(dkey), d['data'][dkey])
            else:
                setattr(self, str(key), d[key])