Segments local networks

.ancestors, descendents, family/network Allows you to query an ID and get the IDs of related segments in its local drainage network

Also consider adding segments.isnested, or something similar. This indicates whether segments are in a nested network. Can be combined with the "terminal" option to only return results for terminal outlets.

May need to update isterminus, parents, child, to be functions. Default is to return all info as before, but also not include options to query specific IDs and indices.