Two new functions

Hey Graham, I added two new functions. I wasn't sure where the proctree should go, but I felt for now system.shl would be a good fit. Let me know what you think!

cpanel.shl

The function cpuser_docroot() provides the document root for a specified domain.

system.shl

The function sys_proctree() provides a consistent means of getting the parent PID of a PID or a process name. From there, it prints the process tree. There can be levels of child processes so it was necessary for the loop.