Created a new version of a Stackable Filament Rack.

Based on feedback and my own experience of another model I've made some changes:

• Simple clean design
• Greater height between racks (previous version was too narrow causing rolls to hit the rack above it. 
• Created a top cap so a shelf can be place on top - I use mine for a filament dryer. 

Original is created with a 26mm hole (approximately 1 inch), which is an easy dowel size to get at any hardware store (at least in Canada). If you need another size because of what is available to you, or because you are spanning a greater distance - let me know what size you need. The model is created in such a way that creating a version with a different hole size (while maintaining integrity and strength) should be easy to do.