polygon2

polygon 2d functions

```rust extern crate polygon2;

use polygon2::{area, triangulate};

fn main() { let points = [[1.0, -1.0], [1.0, 1.0], [-1.0, 1.0], [-1.0, -1.0]];

assert_eq!(triangulate(&points), [0, 1, 2, 0, 2, 3]);
assert_eq!(area(&points), 4.0);

} ```