basic markup & styles

create divs for images, set display properties and initial positioning
add event listeners to app.js

mouseenter on .ryu div:
hide still image and shows ready
mouseleave on .ryu div
opposite behavior
add mouse events to app.js

mousedown and mouseup now hide and show correct images
animate and play hadouken sound

add audio element to main.html
animation and playHadouken fund add to app.js
add keydown behavior
move ryu-swapping to swapRyu function