ps 1.8.0

• New ps_apps() function to list all running applications on macOS.

• New function ps_disk_io_counters() to query disk I/O counters
  (#145, @michaelwalshe).

• New ps_fs_info() to query information about the file system of one
  or more files or directories.

• New ps_wait() to start an interruptible wait on multiple processes,
  with a timeout (#166).

• ps_handle() now allowes a numeric (double) scalar as the pid, as long
  as its value is integer.

• ps_send_signal(), ps_suspend(), ps_resume(), ps_terminate(),
  ps_kill(), and ps_interrupt() can now operate on multiple processes,
  if passed a list of process handles.

• ps_kill() and ps_kill_tree() have a new grace argument.
  On Unix, if this argument is not zero, then ps_kill() first sends a
  TERM signal, and waits for the processes to quit gracefully, via
  ps_wait(). The processes that are still alive after the grace period
  are then killed with SIGKILL.

• ps_status() (and thus ps()) is now better at getting the correct
  status of processes on macOS. This usually requires calling the external
  ps tool. See ?ps_status() on how to opt out from the new
  behavior (#31).