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, I didn't mean to suggest using exceptions, _per se_, just that maybe the appropriate error should be returned (or however that's done in ObjC—usually you pass in a pointer to pointer to NSError, and set it, right?). But as @vokal-isaac explained, these asserts are just here for dev purposes and don't end up in the final build.