Remove Python 2 support completely

I think this was a bad idea. Even if this program is nothing big at all,
but Python 2/3 compatibility is a PITA even for basic tasks (like a
import).

If you need Python 2 support, you can try 3to2. Not gonna guarantee that
it works though, because I want to use the modern features and libraries
from Python 3.
Better error handling, some cosmetic fixes

Now when the user select an invalid stream quality, print all available
stream qualities to user, so he can try again with the correct name.
Bump version