Track-following

Been working on a proof-of-concept for having trains follow tracks in 2D.

Currently this does not use splines of any kind, but simple linear interpolation dense enough to emulate corners.

The major head-scratcher has not been following the track (which is simple) but correct placement of carriages behind the train head - so that they remain consistently spaced. I think I have a plan for this now and need to re-work this prototype.

I'm also keen to try and emulate the 'delayed pull' effect that happens on real train carriages, but this is not yet implemented.