added _weakref mixins

mixin/_weakref.py

@@ -0,0 +1,8 @@
+def proxy(object, callback=None):
+    return object
+
+class ref():
+    def __init__(self, object, callback=None):
+        self.__object = object
+    def __call__(self):
+        return self.__object

test/completion/std.py

@@ -18,3 +18,16 @@ next(re.finditer('a', 'a')).start()
 
 #? str()
 re.sub('a', 'a')
+
+# -----------------
+# ref
+# -----------------
+import weakref
+
+#? int()
+weakref.proxy(1)
+
+#? weakref.ref
+weakref.ref(1)
+#? int()
+weakref.ref(1)()