Added setVolume (windows only)

Implemented setVolume for windows (As I don't own a Mac I can't really
update the OSX part).
Introduced 'property', which allows commands to carry a property
separated by a space character.
Removed unnecessary 'result'-variable and fixed a typo.

index.js

@@ -112,4 +112,8 @@ Playback.prototype.fadeIn = function(callback) {
     this.runTransportScript('fadein', callback);
 };
 
+Playback.prototype.setVolume = function(volume, callback) {
+    this.runTransportScript('setvolume ' + volume, callback);
+};
+
 module.exports = new Playback();

windows_scripts/iTunes.js

@@ -16,7 +16,7 @@ var isRunning = function() {
 };
 
 var getCurrentTrack = function() {
-    var result, currentTrack ;
+    var currentTrack;
     if (isPlaying()) {
         currentTrack = iTunes.CurrentTrack;
         return JSON.stringify({
@@ -97,13 +97,19 @@ var commands = {
             };
         }
         return JSON.stringify({ok: true});
+    },
+    setvolume: function(volume) {
+        iTunes.SoundVolume = volume;
     }
 };
 
-var command = WScript.Arguments.Item(0);
+var args = WScript.Arguments.Item(0).split(' ');
+var command = args[0];
+var property = args[1] || null;
+
 
 if (commands[command]) {
-    WScript.echo(commands[command]());
+    WScript.echo(commands[command](property));
 } else {
     WScript.echo(JSON.stringify({error: "Unsupported command"}));
 }