constructor takes a keyword table, so it can be used for arbitrary DSN
    syntax files of your own chosing.  Simply create an enum {} with all your
    unique tokens in it.  Then create a KEYWORD table.  See SPECCTRA_DB::keywords[].
    The reason you want an enum is to give the C++ debugger better type information
    so it can show symbolic integer symbols.
  * Factored out common richio.cpp and richio.h
    which is what DSNLEXER uses.
  * Fixed some minor issues with reading circuit descriptor from a *.dsn file.