Support for new track API methods

[GoogleCodeExporter]

track.audiofeatures
track.findbyaudiofeatures
track.getPlaylinks

See, for example:

http://ws.audioscrobbler.com/2.0/?method=track.audiofeatures&api_key=b25b959554e
d76058ac220b7b2e0a026&artist=lady+gaga&track=born+this+way

http://blog.last.fm/2011/12/06/london-music-hack-day-our-audio-api-put-us-in-the
-drivers-seat

Original issue reported on code.google.com by michael....@gmail.com on 7 Feb 2012 at 11:56

[GoogleCodeExporter]

<a 
href="http://ws.audioscrobbler.com/2.0/?method=track.getaudiofeatures&artist=rad
iohead&track=creep&api_key=TODO">`track.getaudiofeatures`</a> returns empty 
info:

    <lfm status="ok">
    <audiofeatures></audiofeatures>
    </lfm>

Same for <a 
href="http://ws.audioscrobbler.com/2.0/?method=track.findbyaudiofeatures&filter[
]=bpm:80:90&api_key=TODO">`track.findbyaudiofeatures`</a>:

But <a 
href="http://ws.audioscrobbler.com/2.0/?method=track.getPlaylinks&artist[]=radio
head&track[]=creep&artist[]=Ramona+Falls&track[]=I+Say+Fever&api_key=TODO">`trac
k.getPlaylinks`</a> works:

Creep Radiohead spotify:track:0KYHSg38GsU1naJ5jh1llP I Say Fever Ramona Falls spotify:track:08f0be1cl0CLrJg9Sbq2bB

Original comment by hugovk@gmail.com on 1 Mar 2014 at 4:12

[GoogleCodeExporter]

I've implemented artist/album/track.getPlaylinks in my fork: 
https://github.com/hugovk/pylast/issues/74

Original comment by hugovk@gmail.com on 4 Mar 2014 at 10:44