Add stride to wireframe/surface

I only have this for PyPlot at the moment, I would be more than happy
to add other backends if people find it useful. Also, if people have
any ideas for aliases, then I would be happy to do that too.

src/args.jl

@@ -214,6 +214,8 @@ const _series_defaults = KW(
     :primary            => true,     # when true, this "counts" as a series for color selection, etc.  the main use is to allow
                                      #     one logical series to be broken up (path and markers, for example)
     :hover              => nothing,  # text to display when hovering over the data points
+    :rstride            => 1,        # array row stride for wireframe/surface
+    :cstride            => 1,        # array column stride for wireframe/surface
 )
 
 

src/backends/pyplot.jl

@@ -31,6 +31,8 @@ const _pyplot_attr = merge_with_base_supported([
     :inset_subplots,
     :dpi,
     :colorbar_title,
+    :rstride,
+    :cstride,
   ])
 const _pyplot_seriestype = [
         :path, :steppre, :steppost, :shape,
@@ -702,8 +704,8 @@ function py_add_series(plt::Plot{PyPlotBackend}, series::Series)
             handle = ax[st == :surface ? :plot_surface : :plot_wireframe](x, y, z;
                 label = series[:label],
                 zorder = series[:series_plotindex],
-                rstride = 1,
-                cstride = 1,
+                rstride = series[:rstride],
+                cstride = series[:cstride],
                 linewidth = py_dpi_scale(plt, series[:linewidth]),
                 edgecolor = py_linecolor(series),
                 extrakw...