Get Iterations History

[rafaelrojasmiliani]

First, I would like to congratulate the contributors of this project. It is a great work.

I would like to ask if there is a canonical way to get the value of the optimization variables for the iterations along the optimization process.
I see that the class ifopt::Problem has a member x_prev which I think it contains the data i desire. But this member is private.
My questions are:

1. Contains x_prev the history of the iterations?
2. Is there a way to get its value?

I think that a const method const std::vector<VectorXd> &GetIterations() const { return x_prev; }; will be usefull. It this solves the problem I can do a pull request.

[Levi-Armstrong]

I think this is reasonable. If you create a PR I will review it.