code: function buildOrder () {
      // convert string to array
      if (typeof this.args.order === 'string') {
          this.args.order = [this.args.order]
      }
      // do nothing if order args not set
      if (!Array.isArray(this.args.order) || !this.args.order.length) {
          return
      }
      // order can be array of strings or array of arrays - if first element
      // in order is array then treat as array of arrays
      Array.isArray(this.args.order[0])
          ? _.each(this.args.order, order => this.buildOrderArray(order))
          : this.buildOrderArray(this.args.order)
  }
docs: @function buildOrder
  
  build list of order clauses
  
  @throws {Error}