Bug fix: _restoredCompletedTransactionsFinished was never initialized. First call to restoreTransactions worked fine, but the following calls to restoreTransactions would notify  RMSKRestoreTransactionsFinished more than once.
Add unit tests for issue #35
Merge pull request #35 from xgil78/bug_fix

Bug fix: _restoredCompletedTransactionsFinished was never initialised.
Use return value to check for success instead of indirect error. Fixes #34.
Increase version
Clarified state of development
Discourage MKStoreKit for iOS 7
Set deployment target to 5.1 and include arm64

Thanks @waynehartman.