Proposed specification for estimation functions

This includes factorization of common code and extensions for (unexpected) structural change

Estimated parameters description

xparam1 is a column n by 1 vector holding the current values of the estimated parameters (n is the number of parameters).

xparam1 becomes parameters_description is a (global?) strucure array (with n lines) describing the estimated parameters with the following fields:

Remark 1. Field ID2 is empty if the corresponding estimated parameter is not a correlation.

Remark 2. Field ID1 is empty if the corresponding estimated parameter is not a correlation or standard deviation.

Remark 3. Period1 and Period2 specify the closed sub sample used to estimate the parameter.

Functions