v1.4.0

• Added the item price discount (BT-147). A new optional priceDiscount
  field on InvoiceLineInput emits ram:AppliedTradeAllowanceCharge inside
  the gross price element, so a line can state the discount that connects the
  gross unit price (BT-148) to the net unit price (BT-146) instead of leaving
  it implied by their difference. Requires grossUnitPrice to be set; the
  amount keeps up to four decimals for sub-cent discounts. Omitting the field
  keeps the output byte-for-byte identical (#15).