Update getting started guide.
Fix for Promotion::Rules::Product

Using Promotion::Rules::Product rules with line item actions (Promotion::Actions::CreateItemAdjustments) was broken when the match_policy was "none".

Closes #5664
Fix for ReimbursementTypeValidator

Return items preferred reimbursement type returns an instance, not a class. Comparison in reimbursement type validator was always returning false.

Closes #5657
Round down on original payment and credit reimbursement types.

Add a bit of leniency in the edge-of-edge cases on multiple reimbursement types and rounding issues. See code comments.

Closes #5656
Line-through ineligible adjustments.

Closes #5668
Require Ruby 2.1+