doc: Use more coding conventions in Object Oriented reference example code. * examples/code/@FIRfilter/FIRfilter.m, examples/code/@FIRfilter/FIRfilter_aggregation.m, examples/code/@FIRfilter/subsasgn.m, examples/code/@FIRfilter/subsref.m, examples/code/@polynomial/display.m, examples/code/@polynomial/double.m, examples/code/@polynomial/get.m, examples/code/@polynomial/mtimes.m, examples/code/@polynomial/numel.m, examples/code/@polynomial/polynomial.m, examples/code/@polynomial/polynomial_superiorto.m, examples/code/@polynomial/polyval.m, examples/code/@polynomial/roots.m, examples/code/@polynomial/set.m, examples/code/@polynomial/subsasgn.m, examples/code/@polynomial/subsref.m: Remove "Function File" from deftypefn. Use names of variables in error messages. Surround invalid items in error messages with single quotes. Use meaningful variable names.

function display (p)

  printf ("%s =", inputname (1));

  a = p.poly;
  first = true;
  for i = 1 : length (a);
    if (a(i) != 0)
      if (first)
        first = false;
      elseif (a(i) > 0 || isnan (a(i)))
        printf (" +");
      endif
      if (a(i) < 0)
        printf (" -");
      endif
      if (i == 1)
        printf (" %.5g", abs (a(i)));
      elseif (abs (a(i)) != 1)
        printf (" %.5g *", abs (a(i)));
      endif
      if (i > 1)
        printf (" X");
      endif
      if (i > 2)
        printf (" ^ %d", i - 1);
      endif
    endif
  endfor

  if (first)
    printf (" 0");
  endif
  printf ("\n");

endfunction