add SongType Support

add Support for "SongType" API of echonest, see: http://blog.echonest.com/post/36215424761/we-are-doing-it-live & http://blog.echonest.com/post/35845347430/christmas-comes-early-to-the-echo-nest

Test cases are pretty useless, were more "test programs" for me ... tell me if I should delete them (and make no tests) or do some better ones ;)