EstCovmat File

Estimate the covariance matrix by making steps on a grid in nd
slb 5 aug 2004
AML 2012, updates to have chance of working with bounded and unconstrained parameters

Overwrites whatever is in propose_matrix with the newly estimated matrix
(In future could add/replace some entries with any better info on the covmat
which is already known.)
Uses the steps from the params.ini file to choose grid