Initial try to form the Jacobian and Hessian matrix for exponential decay.
This can be tried with systemtest: relax -s Relax_disp.test_estimate_r2eff_error
task #7822(https://gna.org/task/index.php?7822): Implement user function to estimate R2eff and associated errors for exponential curve fitting.
Authored by: tlinnet 2014-08-25
Parent: [r25253]
Child: [r25255]
