updated usefull-subroutines

I was playing around and modifiedthe usefull-subroutines.ngc that ships with linuxCNC. I updated it to not require you to pass it tool diameter since that is already known to the machine, and allow you to pass it a %DOC rather than have it hard coded to 50%. I am very new to github, and have never contributed to a real project so I don't want to mess anything up, but I think it is ready to make a pull request on github if that is the best way to try an incorperate the changes

There is a new manual page which might help: linuxcnc.org/docs/2.5/html/code/Contributing-to-LinuxCNC.html

thank you, I will read that while the printer warms up

started working on my own library for ngcgui after discovering how easy it is to do, i figured why not go the whole ten yards