add field access with tests

test/cases/module_def/module_ops.tst

@@ -1,22 +1,28 @@
 module Opers
   int foo(int x)
-    int abba = 5
+    int abba = x + self.index
     return abba + 5
   end
 end
 -- -- --
-s(:expressions, 
-  s(:module,  :Opers, 
-    s(:function,  :int, 
-      s(:name,  :foo), 
-      s(:parameters, 
-        s(:field,  :int,  :x)), 
-      s(:expressions, 
-        s(:name,  :int), 
-        s(:assign, 
-          s(:name,  :abba), 
-          s(:int,  5)), 
-        s(:return, 
-          s(:operator,  "+", 
-            s(:name,  :abba), 
-            s(:int,  5)))))))
+s(:expressions,
+  s(:module, :Opers,
+    s(:function, :int,
+      s(:name, :foo),
+      s(:parameters,
+        s(:field, :int, :x)),
+      s(:expressions,
+        s(:name, :int),
+        s(:assign,
+          s(:name, :abba),
+          s(:operator, "+",
+            s(:name, :x),
+            s(:field_access,
+              s(:receiver,
+                s(:name, :self)),
+              s(:field,
+                s(:name, :index))))),
+        s(:return,
+          s(:operator, "+",
+            s(:name, :abba),
+            s(:int, 5)))))))