AM8 z-axis endstop

I really liked rgaida's endstop for the Anet A8 stock frame but didn't see anything like it for the AM8 frame so I made one. The "lower" part that mounts to the motor is unchanged but there are two "upper" parts depending how you want to attach it to the frame. If you built the AM8 with it's included z-endstop you shouldn't need to buy any extra hardware.