Train dispatcher

These actions let a script work together with the Train Dispatcher, Model Train Script's traffic controller for shared track. Before a train drives a path, the script asks the dispatcher for a clearance. As long as the script holds it, no other script (and no manual move) gets a clearance for an overlapping path.

Action	What it does
Request clearance	Ask the dispatcher for permission to drive a path, and set it.
Release clearance	Give a clearance back, so others can use the track.

By default a script holds at most one clearance at a time, and only that script can release it. When you give a clearance a clearance name while requesting it, a script can hold several clearances at once, and other scripts can release the clearance by that name.