1. Fix some known issues and optimize user experience

✔ Support for retina display iPad.

✔ Added new level 'Death Spiral'.
✔ Removed ads from iPhone/iPod version (screen too small to waste screen real estate). Per suggestion by Blake Patterson of Touch Arcade.
✔ Added HUD indicator to find the fuelling station in the second level. Per suggestion by gunxsword.
✔ Added HUD indicators for bridges yet to be visited in the third level.
✔ Used thicker TTY font for better legibility. Per suggestion by Goran.