simulating:
A + B <=> C -> A + D
or
E + S <=> ES -> E + P

with rate constants k1, k1r and k2 .

the program reads in file "dat.txt"
and uses it for
1. the time points to simulate data
2. the initial conditions (ie peak intensities at time = 0
   "dat.txt" has the format:
   time x0 x1 x2 .. etc
   where x0 is peak0 from nmr data
   where x1 is peak1 from nmr data 
   corresponding to the rate eqn :
   x0 = x1 ( A=B; a 2 state reversible reaction)

the program reads in file "guess.txt"
and uses it for
1. initial guesses of the rate constants to be used in fitting data
2. the format is row vector 
   0.1 0.12 2.1 etc...

upon completion a file named "results.txt" is created with the
optimal rate constants.

upon completion a file named "sims.txt" is created with the 
simulated rate curves give the fitted rate constants from the 
file "results.txt"

run the script "go_xmgr" for a quick overlay plot of 
1. original data  ("dat.txt") 
2. simulated data ("sim.txt")