Game Over screen

Added a game over screen and a sound effect for the player death ( still none for the enemy ones :c )

In the game over screen it's possible to see how much the player scored in the last game and you can choose to continue, restart the game or go back to the main menu. At the moment the score isn't saved, but I will create a record (or even a scoreboard) system in the future.

Also changed the game page's cover to a gif which show the core mechanic of the game and uploaded better screenshots.

In a few updates from now there will be, as every fighting game should have, couch multiplayer ;)

I'm unsure on the visual style I want to achieve, so expect graphic changes to the game and the game page.