More alignment of data structures to DIDL

MS data structures moved to their own module. Unnecessary structures removed. Doc fixes
Adding missing file!
Support for radio stations
Fix unicode bug
Album art URI fix
Remove redundant code
pep8
Revising docs for new data_structures
Renaming all ML* classes to Didl*

--HG--
extra : amend_source : 293245673c1db9c03cc1cf95c67d7851a3bce937
Make sure a compatible track is selected before changing the play_mode
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.
pep8/pylint
get_ml_item renamed to get_didl_object in line with other renames
Code review fixes
Temporarily python 3.2 builds on Travis
Merge pull request #243 from lawrenceakka/align_data_structures

More alignment of data structures to DIDL
Merge pull request #251 from robwebset/Snapshot_PlayMode_Fix

Snapshot: Make sure a compatible track is selected before changing the play_mode