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.cpp

@@ -206,7 +206,7 @@ static void extract_font_metrics(Resolved_font& font)
     }
 }
 
-Resolved_font resolve_font(const std::string& family_name)
+Resolved_font resolve_font(const std::string& family_name, const Locator& loc)
 {
     if (family_name.empty())
         return {};
@@ -222,26 +222,26 @@ Resolved_font resolve_font(const std::string& family_name)
         if (!font.family_name.empty()) {
             extract_font_metrics(font);
             // A DERIVED value: an installed font may shadow a default one, and
-            // which directory won is not readable from ":serif_font Whatever".
+            // which directory won is not readable from ":serif_typeface Whatever".
             // The commonest font question -- "why does it not look like the
             // one I installed?" -- is answered by this line.
-            (void)K::log(1, "Font \"" + family_name + "\": " + base + "/" + dir_name);
+            (void)K::log(1, "Typeface \"" + family_name + "\": " + base + "/" + dir_name);
             return font;
         }
     }
 
     std::stringstream ss {};
-    ss << "The font \"" << family_name << "\" is not installed.\n\n"
-       << "Available fonts:\n";
+    ss << "The typeface \"" << family_name << "\" is not installed.\n\n"
+       << "Available typefaces:\n";
     for (const std::string& name : available_font_families()) {
         ss << "  " << name << "\n";
     }
-    ss << "\nFonts are searched in the directories of the KLAMMERTEXT_FONTS\n"
+    ss << "\nTypefaces are searched in the directories of the KLAMMERTEXT_FONTS\n"
        << "environment variable (colon-separated; default $HOME/.klammertext/fonts)\n"
-       << "and then in the default font set.  To install a font,\n"
+       << "and then in the default set.  To install a typeface,\n"
        << "place its files as <fonts-dir>/" << dir_name << "/*.ttf with a\n"
        << "<fonts-dir>/" << dir_name << ".css declaring its @font-face variants.";
-    throw Argument_error(ss.str());
+    throw Argument_error(ss.str(), loc);
 }