Add convenience function to draw frame

lib/plot.py

@@ -153,6 +153,13 @@ class Plotter:
         self.pen_down = True
         self.position = point
 
+    def draw_frame(self):
+        self.move_to(self.paper.bottom_left())
+        self.line_to(self.paper.bottom_right())
+        self.line_to(self.paper.top_right())
+        self.line_to(self.paper.top_left())
+        self.line_to(self.paper.bottom_left())
+
 
 class SVGPlotter(Plotter):
 
@@ -290,4 +297,8 @@ class MultiPlotter(Plotter):
             plotter.finalise()
 
     def register_plotter(self, plotter):
-        self.plotters.append(plotter)
+        self.plotters.append(plotter)
+
+    @property
+    def paper(self):
+        return self.plotters[0].paper