Implement hypernodes for readings

[tla]

There are very many situations where the same readings have to be grouped differently according to what they are being opposed to. Thus there is a need for "hyper-readings" that contain individual reading units. e.g.

Here, on the one hand, βέλος opposes μέλος, but βέλος ἐστὶ in A and C oppose the transposed βέλος ἐστὶ in B. Thus there needs to be a "hyper-reading" that ties together the AC variant.