Parametric house number plate

Quick parametric design for creating a house number plate to put on your wall/fence.

You know how it goes, wanted a nice house plate and couldn't find one that I liked ... so here it is, entirely made in OpenSCAD (required https://github.com/BelfrySCAD/BOSL2/ to be installed).

The parameters you can change are:
- `PL_LENGTH`, `PL_WIDTH` and `PL_HEIGHT` are the base plate dimensions (length, width, thickness)
- `S_DIAMETER` is the size of the screw hole
- `LEAVE_PLATE` if set to true, the design will have a 20% thick solid back which could be printed in a different color; if set to false, the letters and number will be punched through.
- `FOUR_SCREWS` if set to true, there will be 4 screw holes; if false, only 2 screw holes.
- `STREET_NAME` if set to true, the design will have two text lines; if set to false, just the house number is generated.
- `ROUNDED_CORNERS` to get nicely rounded corners if true, otherwise chamfering will be used.
- `TEXT_LINE_1` is the street name, `FONT_LINE_1