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/block/css/block.css

@@ -1,6 +1,6 @@
 
 p {
-    margin: .5rem 0 .5rem 0;
+    margin: 1ex 0;
 }
 
 .quote {
@@ -15,10 +15,8 @@ p {
     overflow: auto;
 }
 
-.centered {
-    margin-left: auto;
-    margin-right: auto;
-    width: fit-content;
+.center {
+    text-align: center;
 }
 
 .indent {
@@ -49,3 +47,8 @@ p {
 .vfill {
     flex-grow: 1;
 }
+
+.left_right {
+    display: inline-block;
+    width: calc((100vw - 60px) / 2);
+}