Customisable Neva Rail Mount

This is a parametrizable mounting base for a Dagoma NEVA printer. I won't suggest using Customizer because this requires OpenSCAD 2016+. Instead just download the .scad file and use it as a library in your designs.

Example usage:
```
use ;
height = 50;
frameThickness = 5;

nevaRailMount(height, frameThickness);
```

`hight` defines the hight of the mounting bracket, `thickness` defines the widest part of the horizontal cross-section. The provided .stl files demonstrate the generated