`set.dendrogram` - added a "labels_to_char" option.
`untangle` - has a default to method (DendSet)
tanglegram: Changed the deafult in cex_main to 2
   * `untangle_step_rotate_1side` - added "leaves_matching_method" parameter.
   * `entanglement.dendrogram` - changed the default of "leaves_matching_method" to be "labels" (slower, but safer for the user...)
`cutree.dendrogram` - replaces NA values with 0L - adjust the tests.
Rename all.unique to all_unique
Test for Color recycling needed - dendextend_options("warn", TRUE)
Test in set.dendrogram needed - dendextend_options("warn", TRUE)

As well as a few other tweaks.
Fixing how the tests are printed by adding cat("\n")
vignettes: tanglegram
vignettes: Correlation measures - Baker's Gamma Index
vignettes: Cophenetic correlation and Bk plots.
`cutree.dendrogram` - added a parameter (NA_to_0L) to control it. Also, make `Bk` work with cutree(NA_to_0L = FALSE)
Added a dendextendRcpp section. (and removed the not-working ggdendro section)
cutree.hclust - added a dummy parameter
Update various files