Pixel vase

I'm migrating [dotSCAD](https://github.com/JustinSDK/dotSCAD) to [2.0](https://github.com/JustinSDK/dotSCAD/tree/v2). Refactoring code with new features of OpenSCAD 2019.05 is one of my targets.

I also add some new functions to generate pixel-style points. Here's a demonstration.

Because dotSCAD 2.0 uses new features of [OpenSCAD 2019.05](http://www.openscad.org/downloads.html), you have to download the scad file, use OpenSCAD to render and export the model.