Feederbot spool adapter

Here is an adapter for [Chris Milnes'](http://www.makerbot.com/blog/tag/square-helper/) totally awesome [Feederbot](http://www.feederbot.com/). The Feederbot is one of the most useful printer accessories I own, making filament changes for multi-colour prints quick and easy - it also has a cleaning sponge built into the feed head.

Anyway, 2.3kg bulk reels are becoming more popular with vendors, but are just a little large for the Feederbot spool holders, so I designed this adapter to provide support for them.