For assumptions, provide child node data

[zherebjatjew]

Assumptions are to skip/take child nodes, but the system does not provide any info about the child nodes.

Maybe we need to change the signature of assume to

Handler assume(BiFunction<Handler, Handler, Boolean> assumption)

where the former Handler represents the current node, and the latter one is a potential child node.

For now it does not make much sense, as the child handler will not have any information except for name.