We need a diff tool for the new file format #15
Description
The old 1.X file format with linear IDs can be inspected using standard UNIX tools such as diff -u0. The new 2.X format can't be, because a single reconnected lexeme within a tree can change the numbering in the rest of the tree, and a newly connected lexeme that was previously an orphan will cause renumbering of all subsequent trees.
Therefore, we need a tool that ignores these spurious changes and only lists the actual reconnections.