Graph reading/writing routines

Graph.read_graph(int vertex_data_size, int arc_data_size, str fname)

Read graph from plain text file

Graph.write_graph(fname)

Write graph to plain text file

Graph.read_ccdata(int vertex_data_size, int arc_data_size, int v_wgt, str fname)

Read graph in DIMACS clique/coloring format

Graph.write_ccdata(int v_wgt, fname)

Write graph in DIMACS clique/coloring format