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/font/css/font.css

@@ -4,18 +4,23 @@
     --serif: Libre Baskerville, serif;
     --sans-serif: Open Sans, sans-serif;
     --monospace:  Inconsolata, monospace;
-    --sans-serif-scale: 1;
-    --monospace-scale: 1;
 }
 
 body {
     font-family: var(--serif);
     font-size: 1rem;
+    /* One normalization for every family switch: render each font so its
+       x-height is 0.5em (the design's anchor -- EB Garamond comes UP ~19%,
+       Open Sans down ~7%).  Inherited, so headings, code, footnotes and any
+       future rule are covered with no per-site scale factors; this replaced
+       the --sans-serif-scale/--monospace-scale system (build-time metrics,
+       applied at four sites and silently missed everywhere else).  The tex
+       target's equivalent is fontspec's MatchLowercase. */
+    font-size-adjust: ex-height 0.5;
 }
 
 tt, .tt, pre {
     font-family: var(--monospace);
-    font-size: calc(1em * var(--monospace-scale));
 }
 
 h1, h2, h3, h4, h5 {
@@ -23,16 +28,11 @@ h1, h2, h3, h4, h5 {
     font-weight: normal;
 }
 
-h1 {
-    font-size: calc(1.2rem * var(--sans-serif-scale));
-}
-
-h2, h3, h4, h5 {
-    font-size: calc(1.1rem * var(--sans-serif-scale));
-}
+/* Heading SIZES live in sks/section/css/section.css (one ladder, one
+   place); this file assigns only the family. */
 
 p {
-    line-height: 1.3;
+    line-height: 1.5;
 }
 
 .plain {
@@ -50,7 +50,6 @@ p {
 
 .sansserif {
     font-family: var(--sans-serif);
-    font-size: calc(1em * var(--sans-serif-scale));
 }
 
 .ritalic {