Actually generate AppliedPatchSet objects (#250)

* Start actually computing AppliedPatchSet values

* Improve patch_apply documentation and flesh out applied patch code

* Add file link notes

* Stub out where tests for snapshot subsystem will go

* Create baseline tests

* Fix build failure by silencing Clippy

src/snapshot/tests/compute.rs

@@ -0,0 +1,35 @@
+use std::borrow::Cow;
+
+use rbx_dom_weak::RbxInstanceProperties;
+
+use crate::snapshot::{compute_patch_set, InstancePropertiesWithMeta, InstanceSnapshot, RojoTree};
+
+#[test]
+fn reify_folder() {
+    let tree = empty_tree();
+
+    let folder = InstanceSnapshot {
+        snapshot_id: None,
+        metadata: Default::default(),
+        name: Cow::Borrowed("Some Folder"),
+        class_name: Cow::Borrowed("Folder"),
+        properties: Default::default(),
+        children: Vec::new(),
+    };
+
+    let _patch_set = compute_patch_set(&folder, &tree, tree.get_root_id());
+
+    // TODO: Make assertions about patch set using snapshots. This needs patches
+    // to be serializable and also to have ID redactions more readily available.
+}
+
+fn empty_tree() -> RojoTree {
+    RojoTree::new(InstancePropertiesWithMeta {
+        properties: RbxInstanceProperties {
+            name: "ROOT".to_owned(),
+            class_name: "ROOT".to_owned(),
+            properties: Default::default(),
+        },
+        metadata: Default::default(),
+    })
+}