Bug fix and added residual function.
Bug fix and added residual function.

Fixed bug in computation of Julier weights (I was reassigning
kappa).

Added ability to specify a residual function for the state to
handle nonlinear/modular state variables.

aitatanit/filterpy,BrianGasberg/filterpy,rlabbe/filterpy,Censio/filterpy,aitatanit/filterpy,BrianGasberg/filterpy,Censio/filterpy,rlabbe/filterpy