Display the order from an XML file and update its total.
Usage php console.php offer:calculator ../src/Order/Fixtures/3for2.xml --applyOffer php console.php offer:calculator ../src/Order/Fixtures/50off --applyOffer
4.99 + 13.95 + 5.49 = 24.43 24.43 - 4.99 = 19.44
4.99 + 5.50/2 4.99 + 2.75 = 7.74 (7.24 in Acceptance criteria)
Todo Write test for Order Calculator and Order Factory