Two scripts to make sense of huge PRs

[Edward K. Ream]

PR #4487 summarizes all the changes between Leo 6.8.8 and master, the old code. 

This PR changes 614 files! Worse, those diffs involve large numbers of changes to sentinel lines. Leonine scripts to the rescue!

The first comment of the PR contains two Leonine scripts that make sense of all those changes:

The first script diffs the entire PR into a tree of Leo nodes. It takes a few minutes to run. The resulting tree describes all the inserted, deleted, and changed nodes in the PR.

The second script "distills" the first tree into another tree. It takes only a few seconds. The distillation removes all the diff-related cruft. In addition, the script removes all diffs involving sentinel lines. The end result shows all and only the significant changes.

Any Leo dev can use these scripts to see for themselves the results of recent work.

Edward