script : update scripts for better parsing the slic3r gcode file

sometimes the slic3r retract/unretract is not consistent.
correct-retract-on-next-layer.py corrects that

added also author.py and g1tog23.py (from linuxcnc website) to
have all the prerequisits for running the cleanup script in
one location

furthermore I have fixed the removing of some temporary files
which had been commented out for debugging purposes