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)

mac/font_store.h

@@ -3,6 +3,7 @@
 // The Klammertext font store (infrastructure; see font_store.cpp).
 
 #include <string>
+#include "locator.h"
 #include <vector>
 
 struct Resolved_font {
@@ -27,7 +28,11 @@ std::vector<std::string> installed_font_dirs();
 std::string default_font_dir();
 // Every installable font family found across those directories.
 std::vector<std::string> available_font_families();
-Resolved_font resolve_font(const std::string& family_name);
+// The Locator is the DOCUMENT location to blame when the typeface is not
+// installed: without it the "not installed" error cites font_store.cpp,
+// a source location no user can act on (the no-.cpp-location rule).
+Resolved_font resolve_font(const std::string& family_name,
+                           const Locator& loc = Locator::none());
 void install_resolved_font(const Resolved_font& font, std::string output_dir);
 
 // One font file classified by its internal metadata (name table, OS/2).