Modified from the ape function extract.clade, which
sometimes behaves erratically.
Unlike extract.clade, this function supports the extraction of "clades"
that constitute a single tip.
See Also
Other tree manipulation:
AddTip(),
CollapseNode(),
ConsensusWithout(),
DropTip(),
EnforceOutgroup(),
ImposeConstraint(),
KeptPaths(),
KeptVerts(),
LeafLabelInterchange(),
MakeTreeBinary(),
RenumberTips(),
RenumberTree(),
Renumber(),
RootTree(),
SortTree(),
TrivialTree