Better OS X support

[hpique]

RMStore kinda supports OS X already. What's missing is a OS X demo project and support for Mac App Store receipts, which are different.

[inPhilly]

I could be wrong, but as of iOS 7, aren't Mac App Store receipts the same as iOS App Store receipts?

[hpique]

@mommyMe That's right. I wrote the issue before I learned about that. Still, a OS X demo project and build target would be nice addition.

[tbaranes]

Any news about that? Particularly in an update of the Podfile to support OSX