Filament Runout Sensor for Scalar 3D Printers

# Description
This plastic part is a Filament Sensor Module for Scalar 3D printer.
It allows to detect the end of filament and trigger a filament change on firmware side.

# Updates
* 2017.04.02 - Minor fix, the button could sometimes get stuck

# Compatibility
* Compatible with both 1.75 and 3mm filament
* This is compatible with Marlin RC8 firmware.
* Just un-comment the runout sensor section on the firmware (near line 776)

# Stuff needed
All you need is a mechanical switch with