Kickstart a new rewrite of the raidillon engine

Endless refactors, refactor everyday, refactor relentlessly, refactor
every morning, every day, every hour.

raidillon_platform/src/assets.rs

@@ -0,0 +1,11 @@
+use std::path::Path;
+
+pub type ModelHandle = usize;
+
+/// The asset manager trait of Raidillon.
+pub trait AssetManager {
+    /// Loads a gltf model to VRAM.
+    fn load_gltf(&mut self, path: &Path) -> ModelHandle;
+    /// Unloads the loaded model from VRAM.
+    fn unload_model(&mut self, model_handle: ModelHandle);
+}