v2.0

Key changes:

• parallel (un)mount jobs via concurrent.futures
• more robust reachability checking:
  • (nm): retry up to 5 times with 3s delay for mount
  • (nm): unconditionally unmount (the interface is down so trying to reach a host causes more harm than good)
  • (direct): run the checks once for mount and unmount
• command timeouts to avoid blocking
• unmount now tries to unmount gracefully first, after a timeout retries with -f and after another timeout with -l -f
• better function docs