zip parallel edges for nx.DiGraph() in algorithms.graph.merge_paths()
add algorithms.graph.longest_path_weighted_nodes()
use weighted merge_paths() in assembly.allmaps() to replace tsp()
avoid overwriting weightsfile between runs
incorporate weights in assigning scaffolds in assembly.allmaps()
standardize debugging info in assembly.allmaps.path()
remove small values in eigenvector in algorithms.matrix.determine_signs()
allow weights to be applied in longest path in assembly.allmaps
add Weights class to parse weightsfile in assembly.allmaps