message: Fix SpriteBatch link
diff: -//! A [`SpriteBatch`](spritebatch/struct.SpriteBatch.html) is a way to
  +//! A [`SpriteBatch`](struct.SpriteBatch.html) is a way to
  //! efficiently draw a large number of copies of the same image, or part
  //! of the same image. It's useful for implementing tiled maps,
  //! spritesheets, particles, and other such things.
  