added method to match the Matplot step for Axis

include/matplotlibcpp17/axes.h

@@ -139,6 +139,9 @@ public:
   // plot
   ObjectWrapper plot(const pybind11::tuple &args = pybind11::tuple(),
                      const pybind11::dict &kwargs = pybind11::dict());
+  // step
+  ObjectWrapper step(const pybind11::tuple &args = pybind11::tuple(),
+                     const pybind11::dict &kwargs = pybind11::dict());
 
   // plot_surface
   ObjectWrapper plot_surface(const pybind11::tuple &args = pybind11::tuple(),
@@ -277,6 +280,7 @@ private:
     LOAD_FUNC_ATTR(legend, self);
     LOAD_FUNC_ATTR(pcolormesh, self);
     LOAD_FUNC_ATTR(plot, self);
+    LOAD_FUNC_ATTR(step, self);
     LOAD_FUNC_ATTR(quiver, self);
     LOAD_FUNC_ATTR(quiverkey, self);
     LOAD_FUNC_ATTR(scatter, self);
@@ -322,6 +326,7 @@ private:
   pybind11::object legend_attr;
   pybind11::object pcolormesh_attr;
   pybind11::object plot_attr;
+  pybind11::object step_attr;
   pybind11::object plot_surface_attr;
   pybind11::object plot_wireframe_attr;
   pybind11::object quiver_attr;
@@ -554,6 +559,12 @@ ObjectWrapper Axes::plot(const pybind11::tuple &args,
   pybind11::object ret = plot_attr(*args, **kwargs);
   return ObjectWrapper(std::move(ret));
 }
+// plot
+ObjectWrapper Axes::step(const pybind11::tuple &args,
+                         const pybind11::dict &kwargs) {
+  pybind11::object ret = step_attr(*args, **kwargs);
+  return ObjectWrapper(std::move(ret));
+}
 
 // plot_surface
 ObjectWrapper Axes::plot_surface(const pybind11::tuple &args,