TAR: Implement extraction and archiving of hardlinks.

[wilx]

This implements hardlinks in TAR. There is also a test to prove it.

[wilx]

My intention with this is to be able to create TAR archives with hardlinks with maven-assembly-plugin.

However, I am not sure if this is the best possible way to do this. I am not sure if it fits right into the PlexusIoResource framework.

[plamentotev]

Also we need to be extra careful when extracting multiple copies instead of creating hard links. If a tar file contains single 1 MB file and thousands of hard links, then extracted (if files are copied) could be 1 GB, possibly resulting in DoS attack.

[wilx]

FYI, I will not be pursuing this pull request further. I was curious if it could be done. But it is unclear to me how to do this so that it matches all the requirements and design criteria of the library. Feel free to pick it up or close it.