Introduce OAuth response and exception

This PR is the second step in order to fix widop/twitter-rest#33. Now, the `sendRequest` method returns a `OAuthResponse` which wraps the original http response and some convenient method in order to easily access usefull informations.

Additionally, it introduces the `OAuthException` which wraps an `OAuthResponse` allowing to have a more complete access to the informations related to the error.