code: function getRatioString(width, height) {
      var d = gcd(width, height);
      var ratio = Math.floor(width/d) + '/' + Math.floor(height/d);
      return ratio;
  }
docs: /*
  makes a string like "16/9" or "4/3" from any width/height combination
  
  combinations with the same ratio will return the same string