Unicode sequences, @typeface, and the font/typeface distinction

A run of Unicode code points now needs one pair of carets, not one pair
each: ^9053 53EF 9053^ renders the characters adjacently, and a single
character inside such a run stands for itself.  An invalid code point is
an error naming the position that wrote it, rather than an apology
rendered into the finished document; noncharacters are refused alongside
surrogates; and a code point that lands on a Klammertext special is safe
through the re-reads that assemble a document.  The character tables now
produce the precomposed form, so a diacritic written as ^a" and one typed
directly are the same text to a search or a copy-paste.

"kdesc -u" describes how to write a Unicode character, with tables of
glyphs beside the codes that produce them.  It is new and not yet
complete: it predates the sequence form and the typeface klammer below.

A typeface and a style are no longer both called "font".  A typeface is a
family resolved by name; a style code is the one letter naming a type
style.  So @document takes :serif_typeface and its siblings, a table takes
:style, captions take :caption_style and :caption_size, the uniform scale
is :text_scale, and the command is "kdesc --typeface".  This renames
arguments a document may already use; an old name is a located error
rather than a silent omission.

@typeface sets a passage in another typeface for the length of that
passage:

    @typeface Noto Sans Egyptian Hieroglyphs | ^132AA 133CF^ :scale 1.5 @

Writing the klammer is the whole declaration -- the document resolves the
typeface, embeds it in what it produces, and carries its license along.
Two typefaces for scripts no text font covers now ship with Klammertext:
Noto Sans Egyptian Hieroglyphs and Noto Sans Cuneiform.  Every typeface in
the distribution now carries its license file.

(from dev 61e598698891)

sks/target/latex_util.h

@@ -6,6 +6,14 @@
 
 namespace latex {
 
+// A fontspec declaration: "\<command>[Path=...,Scale=...]{<regular>}".
+// The command is "setmainfont"/"setsansfont"/"setmonofont" for the
+// document's three role typefaces, and "newfontfamily\ktface<n>" for a
+// typeface a @typeface klammer asked for (a switch command rather than a
+// permanent change).
+std::string font_command(const std::string& command, const Resolved_font& font,
+                         float scale);
+
 std::string page(const std::string& structure,
                  const std::string& title,
                  const std::string& subtitle,
@@ -23,10 +31,10 @@ std::string page(const std::string& structure,
                  const std::string& cover,
                  bool landscape,
                  const std::string& body,
-                 Resolved_font serif_font = {},
-                 Resolved_font sans_font = {},
-                 Resolved_font mono_font = {},
-                 float font_scale = 1.0f);
+                 Resolved_font serif_typeface = {},
+                 Resolved_font sans_typeface = {},
+                 Resolved_font mono_typeface = {},
+                 float text_scale = 1.0f);
 }
 
 void check_for_xelatex();