Improvements to plot2d



Hi,
I have committed a new version of plot2d that introduces several
changes:
  o New options xlabel, ylabel, legend and style.
  o If no labels are given for the axes, some will be created from the
    information given in the command line.
  o Start of a more unified scheme for Gnuplot and Openmath, that might
    be easier to extend to other graphics programs. There are two new
    files gnuplot.lisp and openmath.lisp with functions that do
    equivalent things in the two cases.
  o Reduction in the use of global variables. logx and logy are no
    longer global options. gnuplot_curve_styles and
    gnuplot_curve_titles are no longer used. I will soon replace them
    in plot3d too, so we can eliminate them from the global variable
    plot_options.

I also removed function openplot_curves which is now obsolete because
  plot2d([discrete,...],[plot_format,openmath])
does the same thing with many advantages.

The documentation and figures for the manual are already updated to
reflect the changes. You can see the new look of plot2d in the
examples in the manual:
 http://maxima.sourceforge.net/docs/manual/en/maxima_8.html

There is now a README file in doc/info/figures that explains how to
make new figures for the manual.

Openmath is full of bugs, which I will now start to fix.

Regards,
Jaime Villate