Parametric L-bracket (with rounded edges)

Unfortunately this can't be a Customizer as Thingiverse doesn't support the [scad-utils](https://github.com/openscad/scad-utils) library, you can edit it in [OpenSCAD](http://www.openscad.org/) itself though.

I recently found the scad-utils morphology library and wanted a simple design to test chamfers and fillets on, so remixed ketil's bracket to add them both and fix a couple of measurement issues.