Add TEXTCOLORS constant for chat color codes

Author: Trollhunters501

src/main/java/com/github/steveice10/mc/classic/protocol/data/game/ExtNames.java

@@ -60,6 +60,11 @@ public class ExtNames{
    */
   public static final String BULKBLOCKUPDATE = "BulkBlockUpdate";
 
+  /*
+   * Allows customising chat color codes
+   */
+  public static final String TEXTCOLORS = "TextColors";
+
   /*
    * Allows retrieving precise details on mouse clicks
    */