Basic version drawing

[oldlaptop]

• Lower left corner, toggled by F1. Uses essentially the same
  technique as the FPS counter, since I shamelessly stole that
  code. Closes render the game version on screen #27.

[mic-e]

No need to be ashamed about stealing code that's in the same file (except when it would lead to code duplication, which it doesn't). To be compatible with Minecraft's interface, I suggest using F3 instead, and using that to toggle FPS as well.

[mic-e]

Also, minor code issue: the correct place for the Engine::drawing_version default value would be here, to keep in line with the current code (which I don't like; I'd actually prefer the default value to be in the header. Gonna have to change that some time). Oh, and please put your name in the authors list in copying.md.