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/target/css/target.css

@@ -15,11 +15,6 @@
     vertical-align: middle;
 }
 
-.center {
-    display: flex;
-    justify-content: center;
-}
-
 /* -------------------------------------------------------------------------------- */
 
 .bgap {
@@ -179,3 +174,20 @@
     margin: 0 1em 0 1em;
 }
 */
+
+.footnote_in_text {
+      vertical-align: baseline;
+      position: relative;
+      top: -0.4em;
+      font-size: 70%;
+      line-height: 0;
+      padding-left: 1px;
+      font-weight: bold;
+}
+
+.footnote_rule {
+    width: 40%;
+    margin: 3lh 0 .5lh 0;
+    border: none;
+    border-top: 1px solid black;
+}