Salt shaker (OpenSCAD)

**LATEST VERSION**: https://www.thingiverse.com/thing:3548762

A salt shaker, made with OpenSCAD.

The idea was to use the ```linear_extrude``` module with the twist parameter to create a "screw". It turns out that it's not a good idea. That feature is quite messy, create concave surface and it's hard to control.

I found a screw library http://www.thingiverse.com/thing:8793 but I'm not satisfy with the result. It doesn't respect its parameter. The screw is longer then its length parameter, wider than its radius parameter, etc. I will either try to understand the library better, find another one or write my own.

I found an alternative to OpenSCAD called ImplicitCAD, but the project is still quite immature. I will wait before investing time learning that new software.

[2017-03-24] Uploaded version 3. It's the same shaker, but this time it's using my ```helix_extrude``` library (http://www.thingiverse.com/thing:2200395). It's the first time I use that library, so it might hav