Update post-execution article and samples

+ This change is to reflect changes made in https://github.com/RogueException/Discord.Net/pull/1164, where CommandInfo is now passed into the CommandExecuted event as an Optional<T>

docs/guides/commands/post-execution.md

@@ -37,11 +37,10 @@ about the impact in the [FAQ](xref:FAQ.Commands.General).
 
 Enter [CommandExecuted], an event that was introduced in
 Discord.Net 2.0. This event is raised whenever a command is
-successfully executed **without any run-time exceptions** or **any
-parsing or precondition failure**. This means this event can be
-used to streamline your post-execution design, and the best thing
-about this event is that it is not prone to `RunMode.Async`'s
-[ExecuteAsync] drawbacks.
+executed, regardless of its execution status. This means this 
+event can be used to streamline your post-execution design, and the
+best thing about this event is that it is not prone
+to `RunMode.Async`'s [ExecuteAsync] drawbacks.
 
 Thus, we can begin working on code such as:
 

docs/guides/commands/samples/post-execution/command_executed_adv_demo.cs

@@ -1,4 +1,4 @@
-public async Task OnCommandExecutedAsync(CommandInfo command, ICommandContext context, IResult result)
+public async Task OnCommandExecutedAsync(Optional<CommandInfo> command, ICommandContext context, IResult result)
 {
     switch(result)
     {

docs/guides/commands/samples/post-execution/command_executed_demo.cs

@@ -6,7 +6,7 @@ public async Task SetupAsync()
     // Hook the command handler
     _client.MessageReceived += HandleCommandAsync;
 }
-public async Task OnCommandExecutedAsync(CommandInfo command, ICommandContext context, IResult result)
+public async Task OnCommandExecutedAsync(Optional<CommandInfo> command, ICommandContext context, IResult result)
 {
     // We have access to the information of the command executed,
     // the context of the command, and the result returned from the
@@ -20,7 +20,8 @@ public async Task OnCommandExecutedAsync(CommandInfo command, ICommandContext co
 
     // ...or even log the result (the method used should fit into
     // your existing log handler)
-    await _log.LogAsync(new LogMessage(LogSeverity.Info, "CommandExecution", $"{command?.Name} was executed at {DateTime.UtcNow}."));
+    var commandName = command.HasValue ? command.Name : "A command";
+    await _log.LogAsync(new LogMessage(LogSeverity.Info, "CommandExecution", $"{commandName} was executed at {DateTime.UtcNow}."));
 }
 public async Task HandleCommandAsync(SocketMessage msg)
 {