Changes since 0.1.0

1. src/xfig/plot.sl: modified major/minor axis routines to better deal
   with tic marks that span many orders of magnitude for log plots.
2. src/xfig/plot.sl: If a log-axis does not include a point 10^n, then
   use linear tics-marks.
3. src/xfig/plot.sl: Allow major/minor tic positions to be specified.
4. src/xfig/core.sl: Changed the way the colors are indexed to allow
   and allow colors to be specified by index.
5. src/xfig/polyline.sl: pict_scale was using the wrong object.
6. src/xfig/plot.sl: Use \times instead of \cdot for labels in the alt format
7. src/xfig/plot.sl: If a sym qualifier is given, do not draw lines unless
   line is also specified.
8. src/xfig/plot.sl: hplot method added for plotting histograms.
9. src/xfig/plot.sl: get_*_depth functions included a depth argument
10. src/xfig/plot.sl: Avoid the use of (@Array_Type) to create an array.
11. src/xfig/core.sl: Added orange, orange2-4 colors.
12. src/xfig/core.sl: All objects get set_pen_color, set_area_fill,
    set_thickness, set_lines_style, and set_fill_color methods.
13. src/xfig/objects.sl: Added qualifier support to a few functions.
14. src/xfig/polyline.sl: Added "just" qualifier to the xfig_new_pict
    function to specify its local coordinate system origin.
15. src/xfig/ellipse.sl: Fixed some bugs that surfaced when porting
    old code to use this version of xfig.
16. src/xfig/latex.sl: Added qualifier support to allow the "just"
    qualifier to propagate into the xfig_new_pict function.
17. examples/plot.sl: Tweaked some of the examples
18. src/xfig/plot.sl: plot_symbols now uses a polyline_list instead of
    individual polylines.  This makes it run faster when many points
    are involved.
19. src/xfig/core.sl: If an integer is passed to xfig_lookup_color,
    the value returned will be modulo num_colors.
20. src/xfig/polyline.sl: Use xfig_lookup_color in set_color methods.
21. src/xfig/plot.sl: Added "star", "larr", "rarr", "uarr", and "darr"
    symbols.  Also added xfig_plot_get_symbol_names functions.
22. examples/plot/symbol.sl: Rewrote this example.
23. src/vector.c: Modified the "vector" function to avoid an extra
    function when converting numeric value to a double.
24. src/xfig/polyline.sl: Tweaked the polyline_list_bbox method to
    improve performance.
25. src/xfig/plot.sl: added areafill and fillcolor qualifiers to the
    xfig_new_legend function.
26. src/xfig/polyline.sl: pict_scale was not accounting for the
    absolute position of the pict.
27. src/xfig/plot.sl: Added support for plotting via mixed world
    systems, e.g., world12, world21, etc.  Also, world0 may be used to
    refer to device coordinates, which run from 0 to 1.
28. src/xfig/plot.sl: The hplot method will call the shaded histogram
    routine if a fill qualifier is given.
29. examples/plot/world.sl: A new example.  Also some other examples
    were updated.
30. src/xfig/plot.sl: Added shade_region method and updated the
    world.sl example to illustrate its use.
31. src/xfig/plot.sl: When placing the title, account for the x2label.
32. src/xfig/plot.sl: Ignore tic_linestyle qualifier unless gridding.
33. src/xfig/plot.sl: Cleaned up the tic labeling code and added some
    minor tic labels when using log scaling.
34. src/vector.sl: small optimizations
35. src/xfig/clip.sl: Use slang2.2.0 list_to_array.
