Hello Guix!

Attached is a patch to add the SPARTA Direct Simulation Monte Carlo
Software.

There maybe is a problem with the source URL: The URL always points to
the latest version of the source tar ball which is constantly updated
and immediately released by upstream.  This means that the hash of the
source tar ball available at this URL changes several times a month.  Is
this acceptable or does anyone have an idea how this should be handled?

Thank you!