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/contour3.m
+++ b/scripts/plot/contour3.m
@@ -33,7 +33,7 @@
 ## @example
 ## @group
 ## contour3 (peaks (19));
-## hold on
+## hold on;
 ## surface (peaks (19), "facecolor", "none", "EdgeColor", "black");
 ## colormap hot;
 ## @end group
@@ -46,7 +46,7 @@
 ## The optional input and output argument @var{h} allows an axis handle to
 ## be passed to @code{contour} and the handles to the contour objects to be
 ## returned.
-## @seealso{contourc, patch, plot}
+## @seealso{contourc, contour, contourf, patch, plot}
 ## @end deftypefn
 
 function [c, h] = contour3 (varargin)