Added exit capability from the pause screen
Decoupled the updating and rendering
Cleaned up pausing so that it blocks the update loop of the current screen.
Added support for static text
Started adding support for different font styles
Playing around centring the main menu text.
Added a z-index for sprites.
Changed the way that the pause button works
Added a game over screen
Started fleshing out the interface for screen transitions
Implemented a change in a screen's property over time.
Added support for sprite transparency
Fixed the easing function so that it is correctly easing towards the final value.
Started accumulating transparency of sprites based on their parent object.
Implemented transparency for the level generator so that fading will work correctly.