refactor: simplify shell ProcessMatcher declarations.

* lib/specl/std.lua (object_clone): Fetch paramnames from new
object metatable, not prototype.
* lib/specl/shell.lua (ProcessMatcher): Move dummy `matchp`
declaration from here...
* lib/specl/matchers.lua (Matcher.matchp): ...to here.
(Matcher._parmnames, Matcher._parmtypes): Support type-checked
field assignments by default.
* lib/specl/shell.lua (ProcessMatcher._init): Automatically
assign and check types for each object method.
Adjust all callers.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>