Added `remove` method on `Object`

The `remove` method works like the `increment` method of the `Object` class, but instead incrementing it clears a column value.

parse_rest/datatypes.py

@@ -455,6 +455,19 @@ class Object(six.with_metaclass(ObjectMetaclass, ParseResource)):
             }
         self.__class__.PUT(self._absolute_url, **payload)
         self.__dict__[key] += amount
+        
+    def remove(self, key):
+        """
+        Clear a column value in the object. Note that this happens immediately:
+        it does not wait for save() to be called.
+        """
+        payload = {
+            key: {
+                '__op': 'Delete'
+                }
+            }
+        self.__class__.PUT(self._absolute_url, **payload)
+        del self.__dict__[key]
 
     def removeRelation(self, key, className, objectsId):
         self.manageRelation('RemoveRelation', key, className, objectsId)