feat(argtype): :alone - the value of an option written without one

An optional argument has three values: the default (the name is absent),
the argument type's :alone value (the name is written alone), and a
written value.

:alone is declared by the argument type only, never by a klammer's
parameter declaration -- a default is what one klammer means by silence,
but a bare option name must read the same way in every klammer.  The bool
type declares :alone true, which is the whole of the convention that a
bare boolean option means true; there is no boolean special case in the
engine.  A type whose pattern matches running text cannot declare :alone,
since an option's value runs to the next bar or option name and would
swallow the following text.

kdesc and `ktext -m` now show [default: X] and [alone: Y] per argument
type.

In the Standard Klammer Set: @code :number becomes a bool (it was an
untyped string tested only for truthiness, so a bare :number was a
no-op); decimal_mark declares :alone comma; table_hline and table_vline
declare :alone all.  The 35 bools that default false gained the bare form
for free.

Tests: tst/alone_test.sh (21 cases) joins the shipped suite.

(from dev 6024f49c2859)

sks/list/list.py

@@ -158,7 +158,7 @@ def tex_list(K, list_type, items):
     body = "\n\n".join([f"\\item {e}" for e in items])
     command = {'ol' : 'enumerate', 'ul' : 'itemize'}[list_type]
     topsep = '[topsep=0pt]'
-    listsep = '\\setlist{nolistsep}' if K.cmp != 'false' else ''
+    listsep = '\\setlist{nolistsep}' if K.cmp else ''
     result = f'{listsep}\n\\begin{{{command}}}{topsep}\n{body}\n\\end{{{command}}}\n'
     return result