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`.)
Nope.  Like the `XCTAssert*` themselves, they have to be macros for the test failures to appear in the correct (useful) place.  If they were functions or methods, the test failures would appear piled up inside the function/method rather than in-place in the test method.