add field access with tests

test/cases/function_definition/function_return.tst

@@ -1,17 +1,21 @@
 int retvar(ref n)
-  int i = 5
+  int i = n.layout
   return i
 end
 -- -- --
-s(:expressions, 
-  s(:function,  :int, 
-    s(:name,  :retvar), 
-    s(:parameters, 
-      s(:field,  :ref,  :n)), 
-    s(:expressions, 
-      s(:name,  :int), 
-      s(:assign, 
-        s(:name,  :i), 
-        s(:int,  5)), 
-      s(:return, 
-        s(:name,  :i)))))
+s(:expressions,
+  s(:function, :int,
+    s(:name, :retvar),
+    s(:parameters,
+      s(:field, :ref, :n)),
+    s(:expressions,
+      s(:name, :int),
+      s(:assign,
+        s(:name, :i),
+        s(:field_access,
+          s(:receiver,
+            s(:name, :n)),
+          s(:field,
+            s(:name, :layout)))),
+      s(:return,
+        s(:name, :i)))))