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`.)
The `@try`-`@catch` blocks are, I've read, not particularly performant, but the bigger issue is that you don't necessarily know what low-level (C) stuff is going on in and around the code that might have thrown an exception, so it is not, in general, safe to assume that the environment is in a state that can be recovered when an exception is thrown.  There are some, uh, exceptions to this rule—for instance, there are libraries that throw exceptions in predictable ways that are intended to be caught, but generally such libraries were written by people who were more familiar with language(s) where exceptions could be used for flow control and did not understand that in ObjC, exceptions are generally not considered recoverable.