title: Adding tags to mp3 with eyed3 results in no change
body: <p>I am trying to add tags (title, genre, etc.) to a mp3 file downloaded created with urllib in Python. Using eye3d and the example from their website, the program runs without any errors, but doesn't seem to do anything. When checking the details of the file, title, artist and everything else stays empty as it was before.</p>
  
  <p>Using this example:</p>
  
  <pre><code>import eyed3
  
  audiofile = eyed3.load("song.mp3")
  audiofile.tag.artist = u"Nobunny"
  audiofile.tag.album = u"Love Visions"
  audiofile.tag.album_artist = u"Various Artists"
  audiofile.tag.title = u"I Am a Girlfriend"
  audiofile.tag.track_num = 4
  
  audiofile.tag.save()
  </code></pre>
  
  <p>Am I missing something?</p>