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)

sks/document/document.k

@@ -63,3 +63,20 @@
 @@
 
 @@document.html,tex :: @eval :cpp *KLAMMERTEXT_HOME*/sks/document/document document @ @@
+
+# The following definition of @document.txt is not adequate (it ignores :files,
+# for example), but it enables tests of other txt klammers for now.  When one of
+# the arguments is empty, the justifcation postprocess should remove multiple
+# lines, but __VSPACE__ inserts a space character, which prevents the lines
+# removal from the justification function.  You can also see the extra space
+# before the *subtitle* value.
+
+@@document.txt ::
+@eval "*title*".upper() @ @nl@
+*subtitle*
+
+*author* @nl@
+*date*
+
+*text*
+@@