code: function arrayKV (obj, k, v, reverse, unique) {
    var d = obj[k];
    d = obj[k] = k in obj ? (Array.isArray(d) ? d : [d]) : [];
    if(unique && d.indexOf(v)>-1) return
    reverse ? d.unshift(v) : d.push(v);
  }
docs: ensure obj[k] as array, then push v into it