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

test/cases/root/module_assignment.tst

@@ -0,0 +1,16 @@
+module Fibo
+  a = 5 + foo
+  bar( b , a , r)
+end
+
+-- -- --
+s(:list,  [s(:module,  "Fibo",  [s(:assign, 
+  s(:name,  "a"), 
+  s(:operator,  "+", 
+    s(:int,  5), 
+    s(:name,  "foo"))), s(:call, 
+  s(:name,  "bar"), 
+  s(:arguments, 
+    s(:name,  "b"), 
+    s(:name,  "a"), 
+    s(:name,  "r")))])])