Add darklyrics provider

[skuill]

Website: http://www.darklyrics.com/
Example:

1. Parkway Drive - It's Hard To Speak Without A Tounge: http://www.darklyrics.com/lyrics/parkwaydrive/killingwithasmile.html#8

Note:
The correct URI for the song lyrics can be found on the artist's page. (the similar logic was used in the #38):