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)

sks/date/date.k

@@ -7,9 +7,8 @@
   order, separator, and padding: "6/16/1910" (en, month first),
   "16.06.1910" (de, day first, zero-padded per DIN 5008)
 @@
-@@date.html :: @eval date.date(K) eval@ @@
-@@date.tex :: @eval date.date(K) eval@ @@
-@@date.txt :: @eval date.date(K) eval@ @@
+
+@@date.* :: @eval date.date(K) eval@ @@
 
 @@datetime.k :days.int 0 :lang.language :number.bool false :
   Date and time formatted as "16 June 1910, 13:10" (^:lang de:
@@ -17,21 +16,14 @@
   tomorrow, ^:days -1 is yesterday).  ^:lang and ^:number select the
   language and the numeric form as for ^@date
 @@
-@@datetime.html :: @eval date.datetime(K) eval@ @@
-@@datetime.tex :: @eval date.datetime(K) eval@ @@
-@@datetime.txt :: @eval date.datetime(K) eval@ @@
+
+@@datetime.* :: @eval date.datetime(K) eval@ @@
 
 @@timestamp.k : Date and time formatted as "1910.06.16-12:34" @@
-@@timestamp :: @eval time.strftime("%Y.%m.%d-%H:%M") eval@ @@
+@@timestamp.* :: @eval time.strftime("%Y.%m.%d-%H:%M") eval@ @@
 
 @@serialdate.k : Date formatted as "YYMMDD" @@
-@@serialdate :: @eval time.strftime("%y%m%d") eval@ @@
+@@serialdate.* :: @eval time.strftime("%y%m%d") eval@ @@
 
 @@year.k : Current year formatted as "20XX" @@
-@@year :: @eval time.strftime("%Y") eval@ @@
-
-#[
-@@@category date
-date datetime timestamp serialdate
-:desc Time and date formatting @@@
-]#
+@@year.* :: @eval time.strftime("%Y") eval@ @@