convert_tree2brts: Convert a tree into branching times
Description
Convert a tree into branching times.
Differently from the branching.times function in ape,
it will keep the multiple events. Since the units are million
years, a precision of 8 means that the approximation goes up to the 8-th
digits. With such approximation we consider events happening within an
interval of 4 days (1 million years / 10^8 = 1 year / 100) as simultaneous.