[Gretl-devel] duration functions

I have a student who's working on duration models, and in trying to help him it seemed to me we could do with some functionality to compute nonparametric estimates of the integrated hazard and survival functions. So I've added a couple of built-ins: naalen (Nelson-Aaalen hazard estimate) and kmeier (Kaplan-Meier survival estimate). Basic documentation is also added. I plan to add a section to the User's Guide on using these functions (along with generalized residuals) to assess the specification of a duration model, but that'll have to wait for a while. Allin