Added Async and new Helper Docs

Author: Johnny @PC

docs/SpotifyWebAPI/gettingstarted.md

@@ -59,6 +59,17 @@ if (profile.HasError())
 }
 ```
 
+##Asynchronous
+Every API-Call now has an asynchronous method. Just append `Async` to the Method-Name.  
+Example:
+```cs
+public async void Test()
+{
+    var profile = await _spotify.GetPrivateProfileAsync();
+    Console.WriteLine(profile.DisplayName);
+}
+```
+
 ---
 
 ##API-Reference
@@ -120,3 +131,6 @@ if (profile.HasError())
 ###Tracks
 * [GetSeveralTracks](/SpotifyWebAPI/tracks#getseveraltracks)
 * [GetTrack](/SpotifyWebAPI/tracks#gettrack)
+
+###Util
+* [Utility-Functions](/SpotifyWebAPI/util)

docs/SpotifyWebAPI/util.md

@@ -0,0 +1,15 @@
+##Paging-Methods
+The `SpotifyWebAPI` features two paging-helper Methods, `GetNextPage()` and `GetPreviousPage()`.
+Both are an easy way to receive the next/previous page of a Paging-Object.
+
+Sample:
+````csharp
+var playlistTracks = _spotify.GetPlaylistTracks("1122095781", "4EcNf2l8rXInbJOf3tQdgU", "", 50);
+while (true)
+{
+    Console.WriteLine(playlistTracks.Items.Count);
+    if (!playlistTracks.HasNextPage())
+        break;
+    playlistTracks = _spotify.GetNextPage(playlistTracks);
+}
+````

mkdocs.yml

@@ -14,6 +14,7 @@ pages:
 - ['SpotifyWebAPI/profiles.md', 'SpotifyWebAPI', '- Profiles']
 - ['SpotifyWebAPI/search.md', 'SpotifyWebAPI', '- Search']
 - ['SpotifyWebAPI/tracks.md', 'SpotifyWebAPI', '- Tracks']
+- ['SpotifyWebAPI/util.md', 'SpotifyWebAPI', '- Util']
 - ['SpotifyLocalAPI/index.md', 'SpotifyLocalAPI', 'SpotifyLocalAPI']
 repo_url: 'https://github.com/JohnnyCrazy/SpotifyAPI-NET'
 site_author: 'JohnnyCrazy'