A simple plane cut method for finding a maximum weight independent set. It reads
input files in the DIMACS text format. I.e., they look like this:

c Comment
p edge [num_vertices] [num_edges]
e [v] [u]
....
n [v] [w_v]

For example, the following describes a triangle graph with vertex weights 10, 20
and 30.

c This is a triangle graph
p edge 3 3
e 1 2
e 2 3
e 3 1
n 1 10
n 2 20
n 3 30