Add default value for 'color' in Clear()

This will allow the screen to be cleared without the color parameter being explicitly included (similar to the 2in7 library)

RaspberryPi_JetsonNano/python/lib/waveshare_epd/epd2in13_V3.py

@@ -361,7 +361,7 @@ class EPD:
     function : Clear screen
     parameter:
     '''
-    def Clear(self, color):
+    def Clear(self, color=0xFF):
         if self.width%8 == 0:
             linewidth = int(self.width/8)
         else: