S-mode 2.1

Improvements since last release (unnumbered of Summer 1990):

* Better description provided of functions loaded.

* Better header for this file.

* S-directory is now a prescriptive rather than just
  descriptive variable.

* better syntax table, so |#; are better recognized and
  commands using them work better.

* we have a version number.

Co-authored-by: Ed Kademan <kademan@stat.wisc.edu>
Co-authored-by: Frank Ritter <ritter@psy.cmu.edu>