Quadkey

Converting to and from quadkeys

Usage

```rust use quadkey;

let qk = quadkey::tiletostr(2301, 1305, 14); // 00120211133103

let tile = quadkey::strtotile("00120211133103") // Tile { x: 2301, y: 1305, z: 14}

let qkbin = quadkey::tileto_u64(2301, 1305, 14); // 442897783477764110

let tile = quadkey::u64totile(442897783477764110) // Tile { x: 2301, y: 1305, z: 14} ```