It is not a good idea to have our own submodules named the same way as global ones (e.g., `pyglet`), and I was running into problems with it at some point. For the other ones (e.g., Qt) it probably wouldn't matter, but for the sake of consistency I changed them all. I also prefer "hiding" modules users aren't supposed to get to with underscores, so in my mind it was a win-win.