change test framework to use files for in and out (s-exp)

test/cases/class_def/class_method.tst

@@ -0,0 +1,7 @@
+class Foo < Object
+  int Foo.test()
+    43
+  end
+end
+-- -- --
+{:expression_list=>[{:module_name=>"Foo", :derived_name=>s(:module,  "Object"), :class_expressions=>[{:type=>"int", :receiver=>s(:module,  "Foo"), :function_name=>s(:name,  "test"), :parameter_list=>[], :expressions=>[s(:int,  43)], :end=>"end"}], :end=>"end"}]}