Support for lists/members/destroy_all and destroy by screenName

Added support for Twitter List destroy_all to bulk remove users from lists.

https://dev.twitter.com/docs/api/1.1/post/lists/members/destroy_all

- added 4 flavors of destroyUserListMembers that mirrors createUserListMembers, and a unit test for them.

- added a method to remove a single member from a list by screen name (the id version already existed)

Feedback welcome!