":void" prohibited in prototype argument lists.

Runnable prototypes now accept ":void" only as return types rather than as both
return types and argument lists (as under most conventional high-level
languages). Correspondingly, empty argument lists may still be specified with
the zsh convention for empty lists: "()".

PCRE string global ${ZESHY_PROTOTYPE_RUNNABLE_ATTRS_NAMES_ARGS_PCRE} now
captures the contents of a function's argument list regardless of whether such
list is embedded in an "args = "-prefixed channel or not. Unfortunately, doing
so appears to have introduced prototype validation errors -- to be corrected on
the morrow, by and by.