Write a Singularity unpacker

[remram44]

According to @VickySteeves Singularity is now quite common on HPC clusters. I checked and NYU's new cluster, Prince, has singularity 2.3.1 available.

We should write an unpacker for reprounzip that uses Singularity. I don't expect it would be much work either.

[julianafreire]

What are the differences between docker and singularity?

[remram44]

Singularity does less isolation and is therefore more suitable for HPC environments. It's more about deploying environments than containerizing processes.

It looks like it's easy enough to import a tarball so this should be easy.