CHAP and CTOC frames support (https://github.com/taglib/taglib/issues/81)

I've added support for ID3v2 CHAP and CTOC frames (according to http://id3.org/id3v2-chapters-1.0).

Every field is supported, except optional embedded frames, which  are currently ignored, because I wasn't sure, how to handle them properly.

Also, I added some basic tests of CHAP and CTOC frames parsing.