`wrapped_spline` breaks when `phi` is not between -np.pi and np.pi

[christinahedges]

wrapped_spline is designed to wrap the spline at -np.pi/np.pi, but if you pass in an array that doesn't go between those values, it breaks in a really weird way:

We need some sort of error check to see if the input angle is actually supposed to be wrapped, or we need to make wrapped_spline more robust.