Reception of ODTs in DTOs

My code is receiving ODTs from slave DAQ configuration.

I had to study the pyxcp code to understand that self.cro_callback can be set in order to get notifications on reception of DTOs.

Even though the "workaround" is to just assign a callback method to master.transport.cro_callback, it would be nicer to have a specific API in Master() class to decrease dependency on a specific pyxcp version.

What do you think?

version 0.18.48