add bullet object
mute music
add event listener to instantiate player bullet
bullet update
add bullet.js script
create bullet.js
Set constant enemy num
add enemy object
remove collision for testing.
create Enemy.js object
add enemy object
add enemy object script
modify cloud, enemy constant; add constant state.
Add Level2 state in switch
add collision for enemy and plane
scale up enemy image size
remove commented code
add condition for level2 state
add level2 script
create level2