Artist search

I've added artist search. This allows to you to search for an artist and find album names, find version of those albums and then play them. The keyword ```artist``` is used to query for artists. If multiple artists match the name with a probability of over 85%, you must pick your artist. Example:
```
artist muse
```
```
Which 'muse':
1:	Muse <> New Zealand singer
2:	Muse <> French ambient trance, key track "Innocent Voices"
3:	Muse <> defunct US alt rock band, 97 album "Arcana"
4:	Muse <> Australian duo, "Nat & Kath", track "Fall"
5:	Muse <> UK rock band


Which one to play? [1-5] >
```

Then pick an album
```
Choose album:
1:	1999-09-06 <> Showbiz
2:	2001-06-13 <> Origin of Symmetry
3:	2003-09-08 <> Absolution
4:	2006-06-28 <> Black Holes and Revelations
5:	2009-09-11 <> The Resistance
6:	2012-09-28 <> The 2nd Law


Which one to play? [1-6] > 
```

And finally pick a release:
```
Choose release:
1:	US <> 2012-10-02 <> The 2nd Law
2:	DE <> 2012-09-28 <> The 2nd Law
3:	XW <> 2012-10-02 <> The 2nd Law
4:	FR <> 2012-10-01 <> The 2nd Law
5:	GB <> 2012-10-01 <> The 2nd Law
6:	US <> 2012-10-02 <> The 2nd Law
7:	AU <> 2012 <> The 2nd Law
8:	US <> 2012-10-02 <> The 2nd Law
9:	GB <> 2012-10-01 <> The 2nd Law
10:	GB <> 2012-10-01 <> The 2nd Law
11:	GB <> 2012-10-01 <> The 2nd Law


Which one to play? [1-11] > 
```

If there is only one choice in one of these steps, the step is not shown. For instance the French muse has only one release of one album, thus the tracklist of the album is shown directly:
```
Tracks:
 1  Innocent Voices
 2  Dawn, Part One
 3  Di-li-do
 4  Chant D'amor
 5  Interlude Colour of Night
 6  Colour of Night
 7  Ancient Chorus
 8  Innocent Voices (album version)
 9  Interlude the Shining
10  The Shining
11  Tune From Shopsko
12  Dawn, Part Two
13  Interlude Tune From Pilentze
14  Tune From Pilentze
15  Shopsko Rhapsody

Innocent Voices by Muse

Specify bitrate to match or [q] to abort
Bitrate? [320] > 
```

Tested with Python 2.7.8 and Python 3.4.1 on Arch linux. Not tested on Windows.