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/locator.cpp

@@ -135,3 +135,25 @@ std::string locator_summary(std::vector<Locator> locators)
     }
     return "";
 }
+
+// Parse "[<file>:<line>.<column>]" -- see the declaration in locator.h.
+// Scanned from the RIGHT, because a pathname may itself contain ":" and
+// "." while the line and column never do.
+Locator Locator::from_string(const std::string& s)
+{
+    if (s.size() < 6 || s.front() != '[' || s.back() != ']')
+        return Locator::none();
+    std::string body = s.substr(1, s.size() - 2);
+    size_t dot = body.rfind('.');
+    if (dot == std::string::npos) return Locator::none();
+    size_t colon = body.rfind(':', dot);
+    if (colon == std::string::npos) return Locator::none();
+    try {
+        int line = std::stoi(body.substr(colon + 1, dot - colon - 1));
+        int chr = std::stoi(body.substr(dot + 1));
+        // str() prints m_chr + 1; undo that so a round trip is exact.
+        return Locator(fs::path(body.substr(0, colon)), line, chr - 1);
+    } catch (const std::exception&) {
+        return Locator::none();
+    }
+}