2020 Mountable Optical Filament Sensor

Remixed from the optical filament sensor at http://www.thingiverse.com/thing:1646220 but modified with two M5 holes to allow it to be mounted to a 2020 extrusion.

It uses a no-name optical endstop (like this one http://www.geeetech.com/images/v/Geeetech_IMG_5412.jpg) switch and just "guides" the filament threw it.

Endstop is connected to a Rasperry Pi running Octoprint, which is handing the correct parking and resuming by using the Filament Sensor Plugin http://plugins.octoprint.org/plugin