1.75/6 mm Contractible spool for filament coils

Big thanks [Heinz Spiess](http://www.thingiverse.com/enif/about) for sharing your [design](http://www.thingiverse.com/thing:252808).

I like idea and design of original but it is not suitable for me.

This thing the same as original except two changes:

- Central hole in hub changed to 6 mm but external radius of hub the same.
- Holes for filament fix changed from 3mm to 2 mm (for 1.75 mm filament) but mounting holes unchanged 3 mm.

I made minimal changes in .scad file an describe c