Fix several issues

* Method  ```writeToFile:atomically``` used in ```writeFileDataForObject:``` is deprecated.
* Fixed memory issue with ```error``` and ```@autoreleasepool```. Mentioned here https://github.com/mhausherr/Light-Untar-for-iOS/issues/10
* According to GNU tar specification '\0' is also a file.
* According to GNU tar specification ```filename``` can also be a path.

> The name field is the file name of the file, with directory names (if any) preceding the file name, separated by slashes.