Implemented users/search, users/lookup and fixed incompatibilities with Twitter API 1.1

* I have added a new method users_search for implementing users search functionality (https://dev.twitter.com/docs/api/1.1/get/users/search).

* I have added a new method users_lookup for implementing users lookup functionality (https://dev.twitter.com/docs/api/1.1/get/users/lookup).

* Fixed incompatibilities with Twitter API 1.1 in friendship/destroy and friendship/create.