Utility crate to handle common tasks that require graphs
warning! this crate is not yet complete and the API is yet to change.
```rs
use graph::Graph;
let mut graph = Graph::new();
// insert the numbers 1 to 10 as vertices
for i in 1..=10 {
}
assert_eq!(graph.size(), 10);
// construct a graph satisfying the following condition
// there exists an edge (u, v) if the condition holds