[feat] Autoplay

[ciampo]

• autoplay, autoplay-duration, autoplay-stop-on-interaction attributes
• play() and pause() methods
• a11y (see next comment)
• CSS vars to styles play/pause button

[ciampo]

A11y:

• play/pause button
• Pause on mouseover and focusin; play again on mouseleave and focusout (if the pause button was not pressed)