Move the Rust tutorial into a sub-directory

To make room for the C++ version next to it :-)

docs/tutorial/rust/src/game_logic_in_rust.md

@@ -0,0 +1,74 @@
+# Game Logic In Rust
+
+We'll implement the rules of the game in Rust as well. The general philosophy of SixtyFPS is that merely the user
+interface is implemented in the `.60` language and the business logic in your favorite programming
+language. The game rules shall enforce that at most two tiles have their curtain open. If the tiles match, then we
+consider them solved and they remain open. Otherwise we wait for a little while, so the player can memorize
+the location of the icons, and then close them again.
+
+We'll modify the `.60` markup inside the `sixtyfps!` macro to signal to the Rust code when the user clicks on a tile.
+Two changes to `MainWindow` are needed: We need to add a way for the MainWindow to call to the Rust code that it should
+check if a pair of tiles has been solved. And we need to add a property that Rust code can toggle to disable further
+tile interaction, to prevent the player from opening more tiles than allowed. No cheating allowed! First, we paste
+the callback and property declarations into `MainWindow`:
+
+
+```60
+...
+MainWindow := Window {
+    callback check_if_pair_solved(); // Added
+    property <bool> disable_tiles; // Added
+
+    width: 326px;
+    height: 326px;
+
+    property <[TileData]> memory_tiles: [
+       { image: img!"icons/at.png" },
+...
+```
+
+The last change to the `.60` markup is to act when the `MemoryTile` signals that it was clicked on. We add the following handler:
+
+```60
+...
+MainWindow := Window {
+    ...
+    for tile[i] in memory_tiles : MemoryTile {
+        x: mod(i, 4) * 74px;
+        y: floor(i / 4) * 74px;
+        width: 64px;
+        height: 64px;
+        icon: tile.image;
+        open_curtain: tile.image_visible || tile.solved;
+        // propagate the solved status from the model to the tile
+        solved: tile.solved;
+
+        clicked => {
+            // old: tile.image_visible = !tile.image_visible;
+            // new:
+            if (!root.disable_tiles) {
+                tile.image_visible = !tile.image_visible;
+                root.check_if_pair_solved();
+            }
+        }
+    }
+}
+```
+
+On the Rust side, we can now add an handler to the `check_if_pair_solved` callback, that will check if
+two tiles are opened. If they match, the `solved` property is set to true in the model. If they don't
+match, start a timer that will close them after one second. While the timer is running, we disable every tile so
+one cannot click anything during this time.
+
+Insert this code before the `main_window.run()` call:
+
+```rust,noplayground
+{{#include main_game_logic_in_rust.rs:game_logic}}
+```
+
+Notice that we take a [Weak](https://sixtyfps.io/docs/rust/sixtyfps/struct.weak) pointer of our `main_window`. This is very
+important because capturing a copy of the `main_window` itself within the callback handler would result in a circular ownership.
+The `MainWindow` owns the callback handler, which itself owns a reference to the `MainWindow`, which must be weak
+instead of strong to avoid a memory leak.
+
+And that's it, now we can run the game!