Added a script and log for calculating the numerical covariance matrix for an exponential curve.
This uses the data at http://thread.gmane.org/gmane.science.nmr.relax.devel/6807/focus=6840 and
calculates the covariance matrix via the Jacobian calculated using the numdifftools.Jacobian object
construct and obtain the matrix, both at the minimum and at a point away from the minimum. The
covariance is calculated as inv(J^T.W.J).