Made exception message more readable.
Made exception message more readable.

Added size of the matrix that is incorrectly sized so the user
has some chance of fixing the problem.

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