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/document/document_latex.cpp

@@ -72,6 +72,14 @@ std::string Document_class::tex()
     }
     latex_text = join(lines, "\n");
     latex_text = string_replace(latex_text, "___AT___", "^@");
+    // @typeface: collect what the document asked for, declare each as a
+    // \newfontfamily switch command in the preamble, and replace every
+    // marker with its command.  The declarations are appended to the
+    // prolog, which latex::page emits AFTER \setmainfont -- so fontspec is
+    // loaded and \newfontfamily is valid there.
+    collect_typefaces(latex_text);
+    latex_text = resolve_typeface_markers(latex_text);
+    prolog += typeface_preamble();
     std::string structure_name =
         m_structure == docstruct_t::book    ? "book" :
         m_structure == docstruct_t::article ? "article" : "plain";
@@ -81,5 +89,5 @@ std::string Document_class::tex()
                        point_size, ragged_right,
                        cover, landscape, latex_text,
                        m_resolved_serif, m_resolved_sans, m_resolved_mono,
-                       m_font_scale);
+                       m_text_scale);
 }