Release Name: 0.5.0

Notes:



Changes:
* Warn when encountering nil field instead of raising exception (bug 6446).
* Corrected allowed fields - they are now generated from id3lib's source.
* Renamed :id field to :identifier because of confusion with frame ID.
* Added INSTALL document for installation instructions.
* Fixed memory leak in extension, where iterator was never released.
  According to tests, there is no memory leak anymore.
* Added two patches for id3lib in mswin32 gem:
  * unicode16: fixes Unicode writing bug
  * convert_i-leak: fixes memory leak in Unicode conversion function
* Updated to SWIG 1.3.31.