• Add fetchReceipt method. Update verifyReceipt to use it (#278, related issues: #272, #223).
• Update fetchReceipt and ReceiptValidator to use receipt as Data rather than String. This is consistent with localReceiptData (#284, see #272).
• Remove password from ReceiptValidator protocol as this is specific to AppleReceiptValidator (#281, see #263). Note: This is an API breaking change.
• Unwrap receipt["receipt"]?["in_app"] in two steps (addresses casting problems) (#283, related issue #256).