Made UserAgent configurable and docs

SpotifyAPI.Docs/docs/SpotifyLocalAPI/index.md

@@ -52,6 +52,18 @@ _spotify = new SpotifyLocalAPI(new SpotifyLocalAPIConfig
 });
 ```
 
+it's also possible to change the current `UserAgent` string, which is needed if the library wasn't updated for some time. In this case, you should first make an unauthenticated call with `spotify.GetStatus()`, receive the current spotify version, and update the config afterwards:
+
+```cs
+var config = new SpotifyLocalAPIConfig { Port = 4371, HostUrl = "https://127.0.0.1" });
+_spotify = new SpotifyLocalAPI(config);
+
+var status = _spotify.GetStatus();
+config.UserAgent = status.ClientVersion;
+
+// Now you should call auth stuff, like "_spotify.Connect()"
+```
+
 ## Proxy Settings
 
 You can forward your proxy settings to the local api by using a field in the `SpotifyLocalAPIConfig`.

SpotifyAPI/Local/RemoteHandler.cs

@@ -186,7 +186,7 @@ namespace SpotifyAPI.Local
             {
                 Proxy = _config?.ProxyConfig?.CreateWebProxy()
             };
-            wc.Headers.Add(HttpRequestHeader.UserAgent, "Spotify (1.0.85.257.g0f8531bd)");
+            wc.Headers.Add(HttpRequestHeader.UserAgent, _config?.UserAgent);
 
             return wc;
         }

SpotifyAPI/Local/SpotifyLocalAPIConfig.cs

@@ -10,5 +10,7 @@
         public int Port { get; set; } = 4381;
 
         public ProxyConfig ProxyConfig { get; set; }
+
+        public string UserAgent { get; set; } = "Spotify (1.0.85.257.g0f8531bd)";
     }
 }