Target coverage: a klammer states the targets it serves

kdesc gains --coverage, which reports for every klammer the set of targets it
can render to, and — the point of it — which klammers' coverage cannot be
derived and must therefore be declared.  Three rules: coverage is DERIVED
where the definitions determine it (a general body of klammer calls covers
the intersection of what those klammers cover, by a greatest fixpoint after
loading), DECLARED where the engine cannot interpret what decides it (an
@eval body, whose targets are undecidable), and UNKNOWN where nothing is
written — which never means "deliberately unavailable".

Two new spellings in a definition's name.  A comma-separated target list,
"@@table.html,tex :: ...", gives one body several targets; it is surface
syntax, expanded at registration, and each member goes through the
redefinition rules on its own.  And "@@date.* :: ..." writes the general
target out, asserting that the klammer works for EVERY target including ones
not yet defined — a stronger claim than a list of the targets defined today,
and the one target declaration that could be mechanically falsified.

The Standard Klammer Set was swept accordingly: it now has no general
definitions at all, every klammer names the targets it serves, six use ".*",
and tex and pdf are at zero undecided.

kdesc's flags are reorganised on two rules: a flag reached for often gets a
single letter (-k klammers, -t targets, -c characters, -i input), a more
specialised topic a multi-letter name (--argtypes, --katoms, --rewrite,
--optionsets, --coverage, --klammerset, --font); and -v says how much to show
about PROCESSING, never what the RESULT contains — so the katom regex column
is "--katoms full" and the coverage detail "--coverage all".  NOTE: "-k" now
lists klammers (optionally filtered by a name/description search); the katom
table moved to "--katoms".

Fixes carried along: an option written with no value crashed the command with
SIGSEGV instead of reporting the mistake; two required positional arguments
never parsed; kdesc and kdiag printed an error and exited 0; and definition
diagnostics counted registrations rather than what was written, so one line
could be reported as two definitions and then printed twice.

Four new test suites: target_list, coverage, command_option, kdesc.

(from dev 46f54080bd9a)

mac/util.h

@@ -38,6 +38,19 @@ bool contains(const std::string& str, const std::string& substr);
 bool contains(const std::vector<std::string>& strings, const std::string& element);
 std::vector<std::string> regex_split(const std::string& s, const std::regex& re, bool trim_parts=true);
 std::vector<std::string> word_split(const std::string& s);
+
+// Every run of whitespace becomes one space, and the ends are trimmed.  Needed
+// wherever a phrase typed on one line is matched against text that was written
+// across several: a klammer's description sits on its own lines in a ".k" file
+// and may wrap, so "displayed verbatim" would otherwise match the klammer
+// whose description happens to fit one line and miss the identically worded
+// one that does not.
+std::string collapse_whitespace(const std::string& s);
+
+// Case-insensitive substring test, ASCII folding only.  The project takes no
+// ICU or locale dependency (the same rule as the language tables and
+// ":decimal"), so a non-ASCII query matches only exactly.
+bool contains_fold(const std::string& haystack, const std::string& needle);
 bool is_in(const std::string& s, const std::vector<std::string>& v);
 bool is_not_in(const std::string& s, const std::vector<std::string>& v);
 std::vector<std::string> find_all(const std::string& str, const std::regex& pattern, int match_group=0);