Use IntersectionObserver to turn off renderer when hidden
Use IntersectionObserver to turn off renderer when hidden

Fixes #880

Tyriar/xterm.js,akalipetis/xterm.js,xtermjs/xterm.js,sourcelair/xterm.js,sourcelair/xterm.js,Tyriar/xterm.js,xtermjs/xterm.js,xtermjs/xterm.js,akalipetis/xterm.js,Tyriar/xterm.js,xtermjs/xterm.js,akalipetis/xterm.js,sourcelair/xterm.js,Tyriar/xterm.js,Tyriar/xterm.js,sourcelair/xterm.js,akalipetis/xterm.js,xtermjs/xterm.js