[plt-scheme] some more frtime questions

Hi Greg, all,

I've made some more progress with FrTime/Fluxus - I'm working on some
smaller examples to play with collision detection, and it's going well
so far, using the pong example to learn from.

I'd just like to confirm that I'll need to write a 3D version of posn -
as I can't seem to use scheme vectors as behaviours. Is this because
FrTime supports structs but not vectors as behaviours?

Also, if I want to use fully supported 3D vectors this way, I'm assuming
I won't be able to use the vector maths in fluxus - which is part of a
binary extension.

None of this is a problem at all, I just want to check before I start
writing a lot of code :)

cheers.

dave