Add new simplification rule

This adds the rule “(not F or G) === (F -> G)” to the simplification
rule tableau.

tests/TestHiddenPredicateElimination.cpp

@@ -168,7 +168,7 @@ TEST_CASE("[hidden predicate elimination] Hidden predicates are correctly elimin
 		CHECK(output.str() ==
 			"(s -> not #false)\n"
 			"(t -> not #false)\n"
-			"(not s or t)\n"
+			"(s -> t)\n"
 			"(#false or #false or not #false)\n");
 	}