#39 Optionally re-estimate parameters during LOO cross-validation

[STROH]

Add the possibility to re-evaluate covariance parameters during a Leave-One-Out cross-validation.

[Julien Bect]

Some work is needed to bring the patch up to date with default.

Also, this patch needs to be clarified : it actually does two separate things. First, as advertised, it makes it possible to re-estimate the parameters during LOO-CV. Second, it makes it possible to specify which criterion is used for parameter estimation.

Both are controlled by the same input argument, which is confusing (and prevents from using both options simultaneously).

I think that:

• these two improvements should be done in separate commits to make things clearer;
• each option should have its own dedicated input argument.

[Julien Bect]

Move to github: https://github.com/stk-kriging/stk/issues/9. Closing this ticket.