Transforms the internal representation of a CM back into a version that can be used by Infernal.
Note that models are transformed into
ByteString as-is, the exporter does
not make sure that probabilities add to one, that we write out probabilities
instead of scores, and so on.
TODO some of the notes above will become less problematic once we use newtypes, as a probability-CM will not be accepted by the exporter by then.