Base implementation for the Vagalume lyrics provider
Properly escape unicode escape sequences in JSON

This commit uses more of the Glib library to properly deal with UTF-16
data in a JSON string of the form \uXXXX\uXXXX. Much of the code to
convert the UTF-16 "text" data to UTF-8 was adapted from the json-glib
library.
Merge pull request #33 from fcoelho/provider-vagalume

Added a new lyrics provider (vagalume)