Announcing secr 3.1.5

[murray.efford]

secr 3.1.5 is now on CRAN. You can now view parameter estimates for all levels of a factor covariate simply by setting all.levels = TRUE in predict(). A few bugs are fixed (including the one with binomial count data - see http://www.otago.ac.nz/density/News.html 2017-12-08). Other changes mostly prepare secr to play with a forthcoming package for open population models.