Added update status with media

Hi, I think many people need this feature and I know there is a bunch of pull requests about the same issue, so I took ideas from these other forks.

There are several new features:

* Add status with attached media
* The method can receive as parameter a local file path or a Django File Object

I tried to change code as least as possible and I wrote some tests too, so it would be very easy to merge with master.

If you have any suggest or complaint, I can fix it.