A library to quickly get the live/total/max counts of allocated instances.
```rust
struct Widget {
_c: countme::Count<Self>,
...
}
let w1 = Widget::default();
let w2 = Widget::default();
let w3 = Widget::default();
drop(w1);
let counts = countme::get::<Widget>();
assert_eq!(counts.live, 2);
assert_eq!(counts.max_live, 3);
assert_eq!(counts.total, 3);
eprintln!("{}", countme::get_all());
```