Added depth for rendering system and z value for render components. Still working out kinks in the actual rendering.
More work on #52 . Works correctly. Just need to worry about taking out components after parent entity is destroyed. P.S. Also allows the use of a custom sorting function (if you wanted to sort by y value for a top down view, for instance).
Closes #52 . Removal from the queue will probably be slow. Will look into speeding that up if it ever becomes a bottleneck