v1.9.0

New methods and functions

• ZeroTaxonTree() creates a phylo object with no leaves.

• DropTip() gains new methods DropTip.list() and DropTip.NULL().

• as.matrix.phylo() converts a tree to a matrix representation, allowing
  a tree to be passed as a constraint to ImposeConstraint().

• as.matrix.Splits() and as.matrix.phyDat() methods added as synonyms to
  as.logical.Splits() and PhyDatToMatrix().

Improvements

• Handle TipLabels(0) and BalancedTree(0).

• Support zero-leaf trees in as.Splits() and duplicated.Splits().

• Support non-identical tip labels in as.Splits().

• Try Latin-1 encoding if ReadCharacters() family fail under UTF-8.