Adding TECO command responder.  The comments and formatting have been
taken from the TECO V36 module, which is an ancestor of the TECOCMD.MAR
module that tecocmd.c was based on.  However, the plan is now to use the
old source, 12-Mar-80 MHB as a formatting guide and rebuild the contents
of tecocmd.c into their former self, with TECO V40 changes included.

The V36 module can be found here:

    http://www.ibiblio.org/pub/academia/computer-science/history/pdp-11/teco/rsx/87a/342002/teco.tes

Also includes a round of changes to tecocmd.c, although this will eventually
be replaced by an auto-generated version.