Synopsis
		sflayer < curv.rsf vel= type= s0= s1= twod=n dip= crv=

Parameters
		string crv=   string dip=   float s0= first point   float s1= last point   bool twod=n [y/n] 2-D or 2.5-D   strings type= type of velocity ('c': constant [default], 's': linear sloth, 'v': linear velocity) [nv]   floats vel= velocity [nv]