Added support for removing avatars

src/Discord.Net/DiscordAPIClient.cs

@@ -227,7 +227,9 @@ namespace Discord
 			if (currentPassword == null) throw new ArgumentNullException(nameof(currentPassword));
 
 			string avatarBase64 = null;
-			if (avatar != null)
+			if (avatarType == AvatarImageType.None)
+				avatarBase64 = "";
+			else if (avatar != null)
 			{
 				string base64 = Convert.ToBase64String(avatar);
 				string type = avatarType == AvatarImageType.Jpeg ? "image/jpeg;base64" : "image/png;base64";

src/Discord.Net/DiscordClient.API.cs

@@ -9,6 +9,7 @@ namespace Discord
 {
 	public enum AvatarImageType
 	{
+		None,
 		Jpeg,
 		Png
 	}