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`.)
Yeah, in ObjC, exceptions should not (read: cannot) be used for flow control, like they can in Python.  The assertion macros (`NSAssert`, etc.) throw exceptions, which basically means they crash, so they're for internal and programmer-error stuff, and they turn into no-ops on release builds.