Verbatim-safe typography, ^-punctuation quoting, full-range ^UUUU^, polyglot html

Typographic transforms (---, quote pairs, ~) no longer touch verbatim
text: @c/@code/@source_listing content and ^'...'^ spans show exactly the
characters written. "^" before any punctuation character quotes it in
every target (the apostrophe excepted: ^' opens a literal span), with the
new :resolve option on @@@target declaring per-target renderings. The
^UUUU^ code-point form accepts 4-6 hex digits, the full Unicode range.
The html output and transform spellings are polyglot (XML-valid), in
preparation for an EPUB target. New suites: transform_test, character_test
(engine), typography_test (SKS).

(from dev 07ce5ea86a0a)

mac/klammerset_registry.cpp

@@ -206,9 +206,9 @@ fs::path resolve_klammerset_symbol(
     }
     throw Klammerset_error(
         "The klammerset \"" + symbol + "\" was not found. A symbol x names the "
-        "declaration file x/x.k in one of the search directories: "
-        + join(dirs, ", ")
-        + ". Enter \"kdesc --klammersets\" to list the available klammersets.",
+        "declaration file x/x.k in one of the search directories:\n  "
+        + join(dirs, "\n  ")
+        + "\nEnter \"kdesc --klammersets\" to list the available klammersets.",
         loc);
 }