Confirm throwing in +new: is caught

Refs #78
ARC block/copy issues

This is worrying, but this copy fixes the crash.

I think we probably need to do more copies.

Fixes #77.
An attempt to make the code more readable
Better README examples
SKProductsRequest -> SKRequest

This is how it should have been to start with.
Unwanted Beta 7 fixes

I *know* request.URL can be nil, because I already had a crash here because of it.

I can only hope that when they say they audited for optional compliance they also checked the objective C backing code to ensure nil wasn’t possible there too.
Deprecated subspec warnings
Try to be severe in working around ARC issues

Refs #77
Refs #80
Refs #33

Tag 0.9.16.5
Fix value when manifold was used
NSFileManager+PMKPromise