32 enumerate results using block

This changes the behaviour of CDTQResultSet. Instead of returning results using a for-in loop, it uses the `-enumerateXUsingBlock` pattern.

Amongst other things this should make results easier to consume in Swift.

This doesn't yet move skip and limit to the enumeration loop, for ease of review.

The test changes are trivial, but it might bear checking one or two of them.

Associated issue: #32.
Is the NSString in the comment referring to to the type of objects inside NSArray? If so I think a comment above would make the intention to comment the type of objects inside the array, it appears to me as though the return type was changed.