Finding all Particle Shapes
in a Scene
The MFn::kParticle nodes basically store all of the particles
present in the particle system. It is possible that the particle
system may have a fixed number of particles with no emitters adding
in particles. I assume that this won't happen in my code, though
you may want to check.
All we really need to do to export particle systems is to check
for node connections to the particle shape. Any emitter or dynamics
field nodes we find can then simply be written out to the file.