Ship the escaping test suite; add Provenance to the README

tst/ now carries all three engine regression suites (cond, deftype,
escape) and the Makefile runs them. The README gains a Provenance
section: this repository is a curated snapshot of the private
development tree, stamped with the development commit it was assembled
from.

(from dev f6463478da4c)

README.md

@@ -30,6 +30,17 @@ on).
 Syntax highlighting and editing support for Emacs and Sublime Text are in
 [`doc/edit/`](doc/edit/).
 
+## Provenance
+
+This repository is a curated snapshot of Klammertext's private development
+tree, assembled by a manifest-driven script. Its history is a series of
+release snapshots, not a mirror of the development history, and files here
+are regenerated on each release — patches cannot be merged directly.
+Report problems (or send patches) to the author; accepted changes are
+applied to the development tree and appear in a following snapshot.
+
+This snapshot was assembled from development commit `f6463478da4c`.
+
 ## License
 
 See [`LICENSE.md`](LICENSE.md).