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`.)
Makes sense. I'm honestly not familiar with the patterns for this stuff in Cocoa; in Python we would raise an appropriate exception that would bubble up the call stack. Then we just catch them wherever appropriate. In Go, every function more or less returns data + an error, and so you're always checking `if err != nil` and logging the error and/or handling it in some way.