Dual feed extruder by rcmonitor

>Developed to extrude 3mm (2.85mm) filament via E3D hotend.

>Can be modified to use 1.75mm filament by making appropriate hobbed axles.

>X carriage mounting bolts offset 24mm

###Design goals:
- improve extrusion accuracy;
- improve extrusion stability;
- improve filament reaction;
- increase filament pressure;
- decrease filament slipping possibility;
- increase retraction accuracy;
- increase X-axis available print length;
- provide easier maintenance;
- improve attachement to