message: Add methods to obtain references to internal sprite data in SpriteBatch
  There is currently no way, as far as I know, to remove elements from the
  sprite batch and this would give a decent way of doing that.
diff: @@ -82,6 +82,20 @@ impl SpriteBatch {
  }
  }
  + /// Returns a reference to the sprites.
  + pub fn get_sprites(&self) -> &[DrawParam] {
  + &self.sprites
  + }
  +
  + /// Returns a mutable reference to the sprites.
  + ///
  + /// Please note that manually altering items in this slice
  + /// will not automatically invalidate the buffer, you will
  + /// have to manually call `flush()` or `flush_range()` later.
  + pub fn get_sprites_mut(&mut self) -> &mut [DrawParam] {
  + &mut self.sprites
  + }
  +
  /// Immediately sends all data in the batch to the graphics card.
  ///
  /// Generally just calling [`graphics::draw()`](../fn.draw.html) on the `SpriteBatch`
  