Closes #75

This PR adds a --detail option, which when set will generate a detailed report on the counts of different terms and nodes, grouped depending on the (one of flat, node, term).

• node will group by node types, i.e. iri, bnode
• term will group by term types i.e. subject, predicate
• flat will not reduce the counts, instead concatenating field names, i.e. subject_iri_count

I move some functionality inside FrameInfo in preparation, and I create a subclass FrameDetailInfo, which holds the detail information and the functionality necessary to aggregate the details appropriately.
I also convert MetricsPrinter to a class, as I needed to handle formatting grouping in different ways, I do it by passing the formatter as a constructor argument.