Fully unescape string before decoding base64 to byte[] 

Our server json serializer (Jersey) generates escaped slashes in our byte[]'s base64. I switched to the unsafe string decode when decoding byte[] and added a test that fails otherwise. I added some escape characters to a few other tests along the way and left them in since they make the tests just a pinch more robust.

Thanks a lot for your work on this killer library :)