Add support for WAV

- add support for
  - TagLib::RIFF::WAV::File class
  - TagLib::RIFF::WAV::Properties class

- added swig code for TagLib::RIFF::WAV classes.
- added test code for reading/writing tags (ID3v2)
    to/from WAV files, including cover-arts.
- added a WAV-encoded audio file with ID3v2 tags for tests.
- added documentation.

- Note: support for RIFF-INFO tag is not included,
    TagLib 1.7 does not support this.
I thought that could be a good idea. I wasn't sure how to do it though, TestCase-based or just a plain basic ruby script. Format could be changed. The idea is really to easily validate the examples before copy/pasting to the documentation, or even insert automatically in the documentation without copy/paste if that's possible. Something to think about...