Spool and filament guide

When using full filament rolls the filament can jump outside the roll and snag on the axle. These guides make sure that both the roll and filment stays in place.

Works well with the filament spoolholders: http://www.thingiverse.com/thing:146829

Parts list (except 3dp-parts):
2 M4-screws
2 M4-nuts
1 M4-washer