docs: use async main

* Removed text async

* Updated code

* Added main as proxy task

docs/guides/getting_started/samples/first-bot/async-context.cs

@@ -1,7 +1,6 @@
 public class Program
 {
-	public static void Main(string[] args)
-		=> new Program().MainAsync().GetAwaiter().GetResult();
+	public static Task Main(string[] args) => new Program().MainAsync();
 
 	public async Task MainAsync()
 	{

docs/guides/getting_started/samples/first-bot/complete.cs

@@ -2,8 +2,7 @@ public class Program
 {
 	private DiscordSocketClient _client;
 	
-	public static void Main(string[] args)
-		=> new Program().MainAsync().GetAwaiter().GetResult();
+	public static Task Main(string[] args) => new Program().MainAsync();
 
 	public async Task MainAsync()
 	{

docs/guides/getting_started/samples/first-bot/structure.cs

@@ -10,11 +10,11 @@ using Discord.WebSocket;
 class Program
 {
     // Program entry point
-    static void Main(string[] args)
+    static Task Main(string[] args)
     {
         // Call the Program constructor, followed by the 
         // MainAsync method and wait until it finishes (which should be never).
-        new Program().MainAsync().GetAwaiter().GetResult();
+        return new Program().MainAsync();
     }
 
     private readonly DiscordSocketClient _client;