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/ktype.h

@@ -35,6 +35,16 @@ inline const std::string ws_newline_s { R"(#/\d*)" };
 
 // const std::string k_name = R"([^^@#|\:]+)";
 inline const std::string definition_name = R"([a-zA-Z][a-zA-Z0-9_.]*)";
+// The name at the START of a definition may carry a comma-separated list of
+// targets ("@@table.html,tex"), so its katom runs through commas.  This is
+// deliberately looser than the grammar: the katomizer's job is to delimit the
+// token, and parse_name() in klammer.cpp validates the list, where a
+// malformed one can be reported with its location.  The comma stays out of
+// definition_name itself -- that pattern also delimits klammer APPLICATIONS,
+// option names and "*arg*" variables, where a comma is ordinary writer text.
+// "*" is here for the same reason: "@@date.*" declares a klammer for every
+// target explicitly, and "*" is a Klammertext special everywhere else.
+inline const std::string definition_begin_name = R"([a-zA-Z][a-zA-Z0-9_.,*]*)";
 
 
 enum class katom_t {
@@ -163,7 +173,7 @@ std::vector<Ktype> katom_types {
     Ktype(katom_t::apply_begin, "apply-begin", at_s + definition_name, "Beginning of a klammer call"),
     Ktype(katom_t::apply_end, "apply-end", "(" + definition_name + ")?" + at_s, "End of a klammer call"),
     Ktype(katom_t::option_name, "option-name", ":" + definition_name, "Optional argument name"),
-    Ktype(katom_t::define_begin, "define-begin", at2_s + definition_name, "Beginning of a klammer definition"),
+    Ktype(katom_t::define_begin, "define-begin", at2_s + definition_begin_name, "Beginning of a klammer definition"),
     Ktype(katom_t::define_end, "define-end", "(" + definition_name + ")?" + at2_s, "End of a klammer definition"),
     Ktype(katom_t::klammer_default, "klammer-default", "::::", "Define klammer default value for possible override"),
     Ktype(katom_t::klammer_override, "klammer-override", ":::", "Override existing klammer definition"),