add get_is_valid() checks; move destructor of Rotation3D to header; add documentation
inline key accessor functions from Model and Particle for faster performance
add option to access certain refiner particles by ref for speed + documentation
add validity tracking for Decorator + slight speedup for ScoreState thru cached string
make timer statistics a bit faster by using function header by_refing
minor change to Diffusion
cache particles in FixedRefiner and allow access by ref + allow CentroidOfRefined and WeightedDerivativesToRefined to rely on that speedup
inline key functions in rigid_bodies ; minor documentation ; check rigid body validity before show
fix IMP_DOXYGEN symbol