Verbatim-safe typography, ^-punctuation quoting, full-range ^UUUU^, polyglot html

Typographic transforms (---, quote pairs, ~) no longer touch verbatim
text: @c/@code/@source_listing content and ^'...'^ spans show exactly the
characters written. "^" before any punctuation character quotes it in
every target (the apostrophe excepted: ^' opens a literal span), with the
new :resolve option on @@@target declaring per-target renderings. The
^UUUU^ code-point form accepts 4-6 hex digits, the full Unicode range.
The html output and transform spellings are polyglot (XML-valid), in
preparation for an EPUB target. New suites: transform_test, character_test
(engine), typography_test (SKS).

(from dev 07ce5ea86a0a)

mac/command.cpp

@@ -9,7 +9,16 @@ using namespace std::string_literals;
 
 fs::path construct_command_pathname(char* command)
 {
-    return fs::path(fs::current_path().string() + "/" + std::string(command));
+    // The pseudo source file for command-line string input (-s, kdiag's
+    // input): a file IN THE CWD named after the command, so that a relative
+    // @read in string input resolves against the directory the user ran the
+    // command from -- the string-input analog of "a document's relative
+    // names resolve against the document".  The basename matters: the
+    // former "<cwd>/<argv[0]>" string concatenation anchored resolution at
+    // the BINARY's directory whenever argv[0] was absolute
+    // (/usr/local/bin/ktext, a wrapper script), so every relative @read in
+    // -s input searched bin/ instead of the cwd.
+    return fs::current_path() / fs::path(command).filename();
 }
 
 void set_verbose_level(int argc, char* argv[])
@@ -124,7 +133,7 @@ void load_klammersets(Machine& machine, const strings_t& symbols)
             "The klammerset \"none\" cannot be combined with other klammersets: "
             "it means that none is loaded. Give \"none\" alone, or name only the "
             "klammersets to load.",
-            Locator());
+            Locator::none());
     }
     if (symbols.empty()) {
         // Which klammerset was loaded, and from where, is a DERIVED value: the
@@ -146,7 +155,7 @@ void load_klammersets(Machine& machine, const strings_t& symbols)
                 continue;
             }
             std::string klammerset_filename = resolve_klammerset_symbol(
-                symbol, machine.m_state.value("K_input_dir"), Locator()).string();
+                symbol, machine.m_state.value("K_input_dir"), Locator::none()).string();
             // Symbol -> file is the search path's answer, and the search
             // path has three stages with shadowing: the file it landed on is
             // exactly what a user cannot read off "--klammersets x".