Python2 to Python3 conversion using 2to3

This enables pyicloud to be used with Python3.
Thanks for your work!
Careful!  You can't use the print function in Python 2.6 without adding this line to the top of files using it --

```
from __future__ import print_function
```

Could I convince you into adding that at the top so we can preserve Python 2.6 support?