Merged branch 'universal-handler'

Now `TableTest::UniversalCases` seems to work and has been
made the default for `Cases` and `ExceptionCases`.  THe original
versions still remain, for now.  These will be retired once
a few more use-cases get tried.

The `UniversalHandler` that implements the per-case entries
in `UniversalCases` is kinda messy right now.  I have to
clean that up; there's a lot of code duplication therein.

string_algorithms.test/0.cc

@@ -42,7 +42,11 @@ static auto init= enroll <=[]
 	{
 		{ "Complete var",
 			{ "$H$ $W$", { { "H", lambaste<="Hello" }, { "W", lambaste<="World" } }, '$' },
-			{}
+			std::nothrow
+		},
+		{ "Complete var",
+			{ "$H$ $W$", { { "H", lambaste<="Hello" }, { "W", lambaste<="World" } }, '$' },
+			std::type_identity< void >{}
 		},
 		{ "Incomplete var",
 			{ "$H$ $W", { { "H", lambaste<="Hello" }, { "W", lambaste<="World" } }, '$' },