grouping-by

This library provides users the possibility of grouping their iterators by any function. It is similar to C# IEnumerable.GroupBy or Java Collectors.groupingBy

Example:

```rust

[derive(Debug, Clone)]

struct Point { x: i32, y: i32, } let array: [Point; 4] = [ Point { x: 1, y: 2 }, Point { x: 1, y: 3 }, Point { x: 2, y: 2 }, Point { x: 2, y: 2 }, ]; asserteq!( [ (1, vec![&Point { x: 1, y: 2 }, &Point { x: 1, y: 3 }]), (2, vec![&Point { x: 2, y: 2 }, &Point { x: 2, y: 2 }]) ] .iter() .cloned() .collect::>>(), array.iter().groupingby(|point| point.x) ); ```