`labels<-.dendrogram` - if value is missing, returning the dendrogram as is (this also affects `set`)
set.dendrogram - changed from using `labels_colors<-` to `color_labels` for "labels_colors" (this will now work with using k...)
set.dendrogram - if "what" is missing, return the object as is.
Changing a dendrogram’s labels

(also added toc, and a bunch of place-holders for other chapters)