Initial implementation of bencode/bdecode pod

Sorry about the length—at least half of the lines are the `xcodeproj` files, but there are still several hundred lines of implementation and several hundred lines of tests.

@vokalinteractive/ios-developers Anyone want to review some code?  (Log any time to `VOKMockUrlProtocol`.)
I suppose for completeness, the asserts should be followed by an `if` test, `NSError` construction, and `nil` return... but these asserts are all in the internal primitive-decoding methods that are all dispatched from a `switch`-`case` on the first character—basically, the asserts are guarding the condition that was just tested before these methods were called—so it felt clumsy to me and the asserts were the minimal guard against my own error (not library-consumer error).