Threaded tap holder

Inspired by [this](https://www.thingiverse.com/thing:2200183) and an upcoming delivery of a dozen more threaded taps, I thought I'd better make a holder for my most-used ones.

I didn't want a hole for the wrench like 2200183 as I have at least three different types/sizes of wrench, so I decided to make the middle hole to fit all of the tiny M1-M2.8 taps I have that are only about 3cm long and under 3mm diameter.

I've not made it a Customizer as I don't think the [threads](http://dkprojects.net/openscad-threads/) library works with that, also there's too many parameters to be practical - like a 2D array of height/diameter for a potentially infinite number of taps! So just download it and pop it into [OpenSCAD](http://www.openscad.org/) if you want to edit it.

I also included a Makefile so you can just call ```make stl``` to get openscad to render+export it.

**Update:** switched to English thread as I couldn't get the scale right with metric: 1.0 was too small, 1.03 way too b