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/block/block.k

@@ -25,11 +25,12 @@ vertical mode is a no-op.
 @@sp.html :: &^#160; @@
 @@sp.tex :: ~ @@
 
-@@footnote.k s : Footnote (TBD) @@
-@@footnote :: [*s*] @@
+# TODO: Easy in LaTeX; how to handle in HTML and plain text?
+# @@footnote.k s : Footnote (TBD) @@
+# @@footnote :: [*s*] @@
 
 @@indent.k s :w.int 3 :linebreak.bool false : Indented block @@
-@@indent :: @eval block.Indent(K) eval@ @@
+@@indent.html,tex,txt :: @eval block.Indent(K) eval@ @@
 
 @@quote.k s :w.int 1 :source : Quotation block @@
 
@@ -40,18 +41,7 @@ vertical mode is a no-op.
 @@
 
 @@quote.tex ::
-ANDY: QUOTE: *s*
-#[
-\hspace*{@{justify.length_mul("|margin|", 1, 'latex')}@}
-\begin{minipage}{\textwidth- @{justify.length_mul("|margin|", 2, 'latex')}@ }
-\raggedright
-|text|
-@? """|source|""" |?
-\vspace*{6pt}
-{\begin{spacing}{1.1}\footnotesize\raggedleft |source| \end{spacing}}
-?@
-\end{minipage}
-]#
+\quoteblock{*s*}{*source*}
 @@
 
 @@quote.txt ::
@@ -61,7 +51,7 @@ ANDY: QUOTE: *s*
 @@note.k s :label Note :color 1.0,1.0,0.9 :bordercolor 0.2,0.2,0.2 :level.int 0 :width
   : Rectangular block for a special note @@
 
-@@note :: @eval block.Note(K) eval@ @@
+@@note.html,tex :: @eval block.Note(K) eval@ @@
 
 @@center.k s : Center text @@
 
@@ -94,11 +84,6 @@ ANDY: QUOTE: *s*
 @@nl.tex :: \newline @@
 @@nl.txt :: \n @@
 
-@@tnl.k : Table newline (deprecated; check) @@
-@@tnl.html :: <br> @@
-@@tnl.tex :: \\\\ @@
-@@tnl.txt :: \n @@
-
 @@newpage.k : Start new page @@
 @@newpage.html :: @@
 @@newpage.tex :: \newpage @@
@@ -128,7 +113,7 @@ only makes some vertical space. @@
 
 
 @@qa.k question | answer : Question and answer formatting @@
-@@qa ::
+@@qa.html,tex,txt ::
 @b Q: @ *question*
 
 @b A: @ *answer*
@@ -139,12 +124,13 @@ only makes some vertical space. @@
 @@block.k : to.coords | content :width.float .5 :point.coords 0.0 0.0
 : Absolute positioning of text block @@
 
-@@block :: @eval block.Block(K) eval@ @@
+@@block.tex :: @eval block.Block(K) eval@ @@
 
 @@lines.k s : Maintain line breaks @@
-@@lines :: @eval block.Lines(K) eval@ @@
+@@lines.html,tex,txt :: @eval block.Lines(K) eval@ @@
 
-@@twocolumns.tex s :
+@@twocolumns.k s : Format *s* in two columns @@
+@@twocolumns.tex ::
 \begin{multicols}{2}
 *s*
 \end{multicols}