title: Using reflection to get a list of all classes that extend a "Solid" class
body: <p>I know how to using Reflection determine the super class of a class.  So if I had a game, and I had a map editor, and I wanted it to have a panel with a button to select select any type of Solid that can be added to the game and add it, I could theoretically use reflection to look through all the classes in my game and see which ones have the super class "Solid", and then add a button to the panel. The only thing that prevents me from doing this is that I need a list of all classes to search through, is there a way I can get that?</p>