Log Message:
Update ruby-taglib to 0.6.0.

## 0.6.0 (2013-04-26)

* Add support for TagLib::MP4 (#3, by @jacobvosmaer)
* Add support for TagLib::ID3v2::Header (#19, by @kaethorn)
* Support saving ID3v2.3 with TagLib::MPEG::File#save (#17)
  *  Note that this requires at least TagLib 1.8, and due to 1.8.0
     having an incorrect version number in the headers, it currently
     requires master. See issue #17 for details.
* Fix segfault when passing a non-String to a String argument
* Documentation updates