Add functions for controlling "like"

This patch adds a function for getting the "like" status of the current
song.  It also changes the "set_like" function to use an event, rather
than just setting it.

libsaria/controls.py

@@ -97,7 +97,10 @@ def toggle_rand():
 	prefs.set_pref("libsaria.random", not prefs.get_pref("libsaria.random"))
 
 def set_like(like=None):
-	sources.set_attr("like", like)
+	return call("SETLIKE", sources.set_attr, "like", like)
+
+def get_like():
+	return sources.get_attrs("like")
 
 def load(file):
 	file = expand(file)