[CRITICAL BUG] Fixed restoration bug caused by incorrectly check for unique identifier for vendor.

Every (re-)installation generates a new unique identifier for vendor.
Every purchase and restoration receipt will be tag with this new unique identifier.
But the latest receipt info might have a unique identifier for vendor from another device, from a previous installation, etc.
So we should only check if the purchase info matches receipt for device for receipt we restored with this device.
We should not check for unique identifier for vendor in latest receipt info.
This has caused a critical bug where restoration will always fails.

This commit attempts to fixed this issue.
Fix warning on CBDateFromDateString function
Merge pull request #24 from lxcid/bug/restoration-always-fails

[CRITICAL BUG] Fixed restoration bug caused by incorrectly check for unique identifier for vendor.
Merge pull request #25 from MaximKeegan/master

Fix Warning for CBDateFromDateString function
Merge pull request #20 from rsanchezsaez/master

Example project is broken after updating AFNetworking
Minor code re-formatting and copy-editing
Adding documentation

Re-arranging methods in implementation
Adding -productsWithRequest:success:failure:
Bumping version to 0.3.0
Fixed rare crash when verifying transactions on iOS 5.1.1.

Maybe this crash is caused by Jailbreak or by malicious users who try to crack IAP. I have not been able to repro it myself, but I have seen reports of it on my deployed App.