Use print_function in example discover.py.
Closes #250
Updated tutorial.rst to reflect the new soco.discover() method.

Closes #248
Merge pull request #252 from petteraas/py3_compatible_discover.py

Use print_function in example discover.py.
Merge pull request #253 from petteraas/update_tutorial_for_discovery

Updated tutorial.rst to reflect the new soco.discover() method.