Create a list of braid IDs containing COMIDs in each braid for a single continguous network
unique_braids.Rd
Find and uniquely identify braids in a network of flowlines, given a dataframe containing comid, fromnode, tonode and divergence as columns. 'find_braids()" identifies braids as cycles in the graph representation of the river network. Internal function for use in 'get_braid_list()'