message: Add weight / vsize
  Weight / virtual size according to BIP141
diff: @@ -191,6 +191,16 @@ Transaction.prototype.hasWitnesses = function () {
  })
  }
  +Transaction.prototype.weight = function () {
  + var base = this.__byteLength(false)
  + var total = this.__byteLength(true)
  + return base * 3 + total
  +}
  +
  +Transaction.prototype.virtualSize = function () {
  + return Math.ceil(this.weight() / 4)
  +}
  +
  Transaction.prototype.byteLength = function () {
  return this.__byteLength(true)
  }
  