router depth gauge parameterized

Easy to print, takes about 10-20 minutes on my mk4s, depending on the size.

Fun thing, I wanted to generate some sizes to upload, I came up with this commandline (linux) to do it:
for i in {1..25}; do openscad --export-format asciistl -D "routerdepth=$i" -o routerdepth-${i}mm.stl routerdepth_gauge.scad ; done

Of course, you can make other sizes as well, just open the customizer in openscad and change the parameters. It can also be used for a table saw or router or other things…

(BTW, my table saw has a slightly lower plate around the blade, so this gauge would have to be much wider to be usable)