FWIW, I plan on writing one for slots on my mill also.
I planned on asking for a code example too. I thought it was just a series of G3's, at least that's my plan on how to write it. I would like to confirm this Once done, just call it up and change tool, start location, end location, width, depth, step over, etc.
Guess I'm old school. nearly all my work is extremely simple gcodes and gcode macros, just LOTS of loops. Plus I design as I go for the assemblies under construction. Sketch what I need, start cutting. write next segment while machine is running.
PS. I would like to know if this method cuts air 1/2 the time with complete G3s. or 180-G3, advance,180-G2, advance. This seems more efficient to me.