Program sfgravcon | Continuation for gravity data by using FFT or intergral iteration 
[SYNOPSIS]
sfgravcon < in.rsf > out.rsf verb=n iter=n z= niter=0
[PARAMETERS]
bool    | iter | =n |  [y/n] | 	if y, perform iteration method 
int     | niter | =0 |   | 	continuation factor allocate memory 
bool    | verb | =n |  [y/n] | 	verbosity flag 
float   | z | = |   | 	for iteration method 
[DIRECTORY]
user/yliu
