PinTree

HashMap/Set<Pin<Arc<T>>> based fully safety tree collection

Examples

```rust let pt = PinTree::::new();

let a = pt.node(1); let b = pt.node(2); let c = pt.node(2);

pt.setparent(b, a); pt.setparent(c, a); // a // ↙ ↘ // b c

asserteq!(pt.isparent(b, a), true); asserteq!(pt.ischild(c, a), true); ```