code: function balance(a, b){
    var diff = a.length - b.length
    var short = diff >= 0 ? b : a
    diff = Math.abs(diff)
    while (diff--) short.push(['c',0,0,0,0,0,0])
    return [a, b]
  }
docs: define `a` and `b` using the same number of
  path segments while preserving their shape
  
  @param {Array} a
  @param {Array} b
  @return {Array}