HOTFEATURE: 2013.5, 2013.4, 2013.2 - Added new "dollar per item" handling fee markup type.

Added new "dollar per item" handling fee markup type. This allows a dollar amount to be applied for each quantity of each line item on the order in the same manner as other handling fees.

For example, we already had a Dollar Per Line Item type; if I had two line items with a quantity of 5 each, and a markup of $5.00, that markup type would apply $10 for the order. With this new markup type, that same scenario would have a markup of $50.00, $5.00 each for all 10 items on the order.