Fixed Step Runge-Kutta

Operates just like ode45 or ode23 except it uses the Runge-Kutta 4 algorithm

This code works very similarly to the ode45, ode23, etc family except it uses the fixed step RK4 algorithm. The inputs are the function handle, the time span, initial conditions and timestep. The extraparameters variable can be used to pass extra information to the derivatives routine rather than using globals. next is a number between 1 and 100 in order to notify the user of the simulations progress. If the variable quat = 'Quat' the simulation will normalize the quaternions assuming the states are (x,y,z,q0,q1,q2,q3,u,v,w,p,q,r).