Helper that will split population definition into chunks of names and operators.
splitn(
definition,
all_names,
operators = c("And", "Or", "Not", "(", ")"),
splitter = "[`~splitter~`]"
)population definition to be splitted
the names of all allowed populations
operators used. Default is c("And", "Or", "Not", "(", ")").
the splitter that will be used to help splitting