[update] asymmetry between gameUpdate and screenUpdate
[update] screenUpdate is looped endlessly
[update] endgame() added
[update] delete useless comments
[update] whole game become 4 stage
[fix] snakes no longer suff when game pause
Merge commit 'b177b152ead1165de19056f88f9bc11ff7ff77f8' into feature-end-screen