Parametric Snap-on Lid

This is a parametric push-fit lid, inspired by [Bar Keepers Friend Cap](https://www.thingiverse.com/thing:2808022). I attempted to scale the aforementioned Thing to fit a cat food container, but it didn't work because in addition to scaling the lid surface, it also scales the lip. I realised I could use make a Thing that takes the dimensions of the container directly, and made this from scratch. Note that this requires a version of OpenSCAD >= [2016.XX](https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/2D_to_3D_Extrusion#Rotate_Extrude) so you will probably have to download and use one of the [development snapshots](http://www.openscad.org/downloads.html#snapshots). Instructions for use locally via OpenSCAD: 1. use a ruler or set of calipers to measure the diameter of your container; 2. download this thing, extract and open `design.scad` file in OpenSCAD; 3. change the value of `container_diameter`; 4. print