DIMACS format

[dstahlke]

DIMACS (or, rather, some extension of the official DIMACS) seems to be a fairly standard graph specification format. I especially see it for lists of graphs for computational challenge problems such as clique finding or chromatic number. Is this format supported by GraphIO.jl? If not, should I add it and submit a pull request?

There are examples and a description of the format here: https://mat.tepper.cmu.edu/COLOR02/

The format has a header starting with "p" that tells the number of vertices and edges, then lines starting with "e" giving the edges. Lines starting with "c" are comments, and there can be other data which could be ignored by a basic reader.

c Lines starting with "c" are comments
p edge 125 736
e 5 1
...