add methods to remove members from list
add contributor
complete the method flavors to match createUserListMembers
Merge commit '7a1811d5cff9782bc2f52d9a938a6e0ca8a8f85b' into list_delete_methods
Merge pull request #104 from HubSpot/list_delete_methods

TFJ-777 Support for lists/members/destroy_all and destroy by screenName