Reference Card: Turtle Graphics

XXX write a reference card of methods

• display a canvas on which turtles run around.
• turtles have various methods: (pick a fixed subset)
• forward/backward/right/left/speed
• pos()/ycor/xcor/heading
• pen/penup/pendown
• hideturtle/showturtle
• home/setpos/setheading
• dot/stamp/clearstamp/reset