Feature Request: Be able to calculate Relative Velocity and Relative Displacement profiles

[subsurfaceiodev]

Like the title says, I'd be really useful to have ProfileBasedOutput classes for Relative velocity and displacements profiles. Just like software like DEEPSOIL presents. Relative displacement profile, for example, at a specific depth is equal to the maximum absolute value of the difference between the displacement vs time of the specific depth and the input motion (at rock).