add option opt_algo to osr

It generally allows integer inputs for a case distinction and also takes a “function_name” string for user-provided files.

It should translate into `options_.osr.opt_algo``

@JohannesPfeifer we can close this issue once you add documentation for this option

@houtanb Could you also allow for handing over the optimizer options via optim as in d27e5bc5?

@JohannesPfeifer to be clear, you mean you want to add the optim option to osr ?

@houtanb Exactly. The OSR code mimics the one in dynare_estimation_1.m. There, we allow passing additional optimizer options via the optim option of the estimation command. I would like to have the same for osr.

@JohannesPfeifer done

@houtanb Thanks. I already documented it. So after merging the pull request, this ticket can be closed.

Closed with #850