Update with media

Hi!

You have very nice lib, by the way :)

I've noticed, that it lacks "update_with_media" so I decided to add it.

The usage is quite straightforward:
```python
api.update_with_media(photo, status=text)
```
photo - is a bytestring like StringIO(file.read()) - it appears to be more convenient for me. If it is a problem, I can change it to a file-like object (or make it optional).

I'm fully ready to add any changes to this solution :)