ISO8601

Since you recommended using the ISO8601 lib for date parsing it seemed appropriate that SSDataKit use it as well. This PR adds Cocoapods to the test project and then updated the `-parseDate:` method to use the ISO8601 lib for when the input was a string.

NOTE: The 2 existing ISO8601 tests now fail, but my added test now passes.
This now fails when using the ISO8601 lib. Here's a comparison of what the old implementation expected vs. what the ISO8601 lib expects. Notice the hours are off.

```
Printing description of date:
2013-06-27 21:45:06 +0000
(lldb) po [NSDate dateWithTimeIntervalSince1970:1372355106]
2013-06-27 17:45:06 +0000
```