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

test/cases/call_site/single_name.tst

@@ -0,0 +1,8 @@
+my_my.foo(42)
+-- -- --
+s(:list,  [s(:call, 
+  s(:name,  "foo"), 
+  s(:arguments, 
+    s(:int,  42)), 
+  s(:receiver, 
+    s(:name,  "my_my")))])