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/Ope