Support for more types of Youtube URLs

Came across links like this http://www.youtube.com/attribution_link?a=vWY_P7tULpw&u=%2Fwatch%3Fv%3DlmpBiqX_DTY%26feature%3Dshare (and http://youtu.be/CSyIrrKhJQQ while testing my modifications). The short links work with making the "watch/embed/v" part optional. Decoding the attribution links seemed the easiest way to make them work. So far, everything I've tried plays now.
In Python 3, unquote() moved to “urllib.parse”, so you should probably used the “compat” module:

```python
from livestreamer.compat import unquote
```