Vignettes: adding a third simulation
added ref to Baker 1974
rank_order.dendrogram function added.

Also moved fix_members_attr.dendrogram to attr_access.r
sample.dendrogram function added. Only works for replace = FALSE
fix_members_attr.dendrogram - fixed a bug introduced by the new "members" method in nleaves. (test added)
More protection for cutree by forcing nleaves to use method order.
nleaves - fix doc.
Fix cor_bakers_gamma to work in case if trees with only leaves.
sample.dendrogram function added - it allows for permutation and bootstrap tests for comparing two trees.
Added a "warn" parameter to cor_bakers_gamma
VIGNETTES: Added a bootstrap and permutation examples for inference on Baker's Gamma.