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

test/cases/while/while.tst

@@ -0,0 +1,16 @@
+while(1)
+  tmp = a
+  puts(b)
+end
+-- -- --
+s(:list,  [s(:while, 
+  s(:condition, 
+    s(:int,  1)), 
+  s(:expressions, 
+    s(:assign, 
+      s(:name,  "tmp"), 
+      s(:name,  "a")), 
+    s(:call, 
+      s(:name,  "puts"), 
+      s(:arguments, 
+        s(:name,  "b")))))])