doc: Improve documentation for 2-D plot functions * doc/interpreter/plot.txi: Rewrite documentation around get/set. * libinterp/interpfcn/graphics.cc(Fget, Fset): Add seealso links. Add additional calling forms for get(). * scripts/plot/bar.m, scripts/plot/barh.m, scripts/plot/comet.m, scripts/plot/comet3.m, scripts/plot/contour.m, scripts/plot/contour3.m, scripts/plot/contourc.m, scripts/plot/contourf.m, scripts/plot/errorbar.m, scripts/plot/gca.m, scripts/plot/gcf.m, scripts/plot/gco.m, scripts/plot/ishghandle.m, scripts/plot/loglogerr.m, scripts/plot/pareto.m, scripts/plot/pcolor.m, scripts/plot/pie.m, scripts/plot/pie3.m, scripts/plot/plotmatrix.m, scripts/plot/plotyy.m, scripts/plot/polar.m, scripts/plot/quiver.m, scripts/plot/quiver3.m, scripts/plot/rose.m, scripts/plot/scatter.m, scripts/plot/semilogxerr.m, scripts/plot/semilogyerr.m, scripts/plot/sombrero.m, scripts/plot/stairs.m, scripts/plot/stem.m, scripts/plot/stem3.m: Improve docstrings.

--- a/scripts/plot/stairs.m	Sat Jun 22 14:36:42 2013 -0700
+++ b/scripts/plot/stairs.m	Sat Jun 22 17:40:52 2013 -0700
@@ -29,9 +29,9 @@
 ## If only one argument is given, it is taken as a vector of y-values
 ## and the x coordinates are taken to be the indices of the elements.
 ##
-## If one output argument is requested, return a graphics handle to the plot.
-## If two output arguments are specified, the data are generated but
-## not plotted.  For example,
+## If one output argument is requested, return a graphics handle to the
+## created plot. If two output arguments are specified, the data are generated
+## but not plotted.  For example,
 ##
 ## @example
 ## stairs (x, y);
@@ -49,8 +49,7 @@
 ##
 ## @noindent
 ## are equivalent.
-## @seealso{plot, semilogx, semilogy, loglog, polar, mesh, contour,
-## bar, xlabel, ylabel, title}
+## @seealso{plot}
 ## @end deftypefn
 
 ## Author: jwe