The V1DataFlow and V5DataFlow classes used a verbose way of unpacking
the hex byte stream to the specific fields until now. With this commit,
both use a list of field names, one struct.unpack call and then a
mapping for-loop for each field.
Additionally the upper boundary of the passed data slice was added.
With the self.__dict__.update() call all fields are now also accessible
as direct attributes of the corresponding instance, e.g. flow.PROTO to
access flow.data["PROTO"]. This works for flows of all three versions.
The tests were adapted to reflect this new implementation.
