adding add/remove methods for collections of behaviours & constraints to VerletParticle2D
adding add/remove methods for collections of behaviours & constraints to VerletParticle2D

--HG--
branch : spatialphysics

postspectacular/toxiclibs,ruby-processing/toxiclibs,rekii/toxiclibs,postspectacular/toxiclibs,rekii/toxiclibs