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/katom.cpp

@@ -131,7 +131,7 @@ void warn_unparsed_katoms(katom_list& katoms, bool warn)
             // commands issue has one format: it said "[warning]" where
             // everything else says "(warning)".
             warning("Word not parsed:\n      " + k.m_text
-                    + "\nTo include a special character (@, |, #, and ^), put "
+                    + "\nTo include a punctuation character literally, put "
                       "\"^\" before it.",
                     k.m_loc);
             k.m_unparsed = false;