Changed performance error on safari
Handled Escape key for pause / resume
Random asteroid generation
Also embiggened asteroids
Corrected tests not passing
Updated CoffeeScript version to 1.6.3
Preparations for viewport
Objects outside the game surface are moved to the other side
Game surface is bigger than the viewport
Viewport now follows the ship
Merge branch 'asteroids'
Merge branch 'collisions'
Merge branch 'screens'
Correct background image resizing
Corrected background shift on horizontal movement.
Resized image to exactly match the game surface.
Added brake / reverse on the ship.
Bit of refactoring on background calculations and ship braking
Top bottom background shifts done; corners remain
Background issue solved
Asteroids are now correctly displayed when the camera is on a corner
Added collisions between asteroids
Simple rebound mechanism