empirical structural functions for circular data described in the vignette register_new_layer_datatype.Rmd

C code doubled omp vs NOomp; extension of turning bands 2D to function as 3D (necessary for spherical models)

updated references in generalised diagonalisations; improved/reimplemented as.logratioVariogram and as.logratioVariogramAnisotropy methods; minor edits at plot.logratioVariogramAnisotropy and variogramModelPlot.logratioVariogram

- url / appropriate usage
- reference in Description