Spiral bitholder

A stand for hex shanked drill bits

This is a remix of hex bit holder by Fitzterra (https://www.thingiverse.com/thing:1686330). However, this remix evolved until it is now almost completely, but not entirely, unlike the original, and has the following features:
* Stepped spiral layout of bits
* Mostly parameterised
* A central hole with a larger clearance for a stepped drill
* Cutouts showing bit size are an artefact of the spiral drawing technique, and go all the way down to the bottom of the bit.
* Hex or round holes
* Extended base for added stability
* Just for fun, the base and centre platform are hexagonal

To do (but probably won't ever get done. Remix it!)):
* Make the outer surface a smooth curve, (and a circular base to match)
* Make the top surface smooth instead of a staircase
* Allow users to optionally add outer sides to the holes
* Parameterize base size
* Fillet corners