added bindingkind verification

test_scoping.sui

@@ -0,0 +1,7 @@
+fn test_scoping() -> int do
+  let x = 5
+  let f = lambda (y) y + 1  # simple lambda
+  f = lambda (z) z+1
+  let x = 10  # shadow x
+  f(3)  # should work
+end