Release Name: 0.2.0

Notes:



Changes:
* Overhauled direct access methods
  * Remove frames by setting them to nil, e.g. tag.title = nil
  * Removed methods for rarely used frames.
  * All methods use strings now, no special cases like track anymore.
  * Explicit call of to_s in set_frame_text.
* More unit tests
* Added method invalid_frames which is useful to detect invalid frame
  data before calling update!.