Add statuses/update_with_media feature

See https://dev.twitter.com/docs/api/1.1/post/statuses/update_with_media

implement support for the update_with_media feature + test.

This code is based on another pull request (https://github.com/tweepy/tweepy/pull/180) but that PR is not compliant with the v1.1 of the Twitter api. 

> Important: In API v1.1, you now use api.twitter.com as the domain instead of upload.twitter.com.

very small code added.

See discussion on issue #119