v0.9.3

Added friction velocity:

gp.wind.FrictionVelocity (non-CF)
gp.wind.XFrictionVelocity (CF)
gp.wind.YFrictionVelocity (CF)
gp.wind.FrictionVelocityDir (non-CF)
gp.wind.FrictionVelocityDirTo (non-CF)

Also connected these as a family