Add file format version

src/lib.rs

@@ -30,5 +30,7 @@ pub mod commands {
 
 #[derive(Serialize, Deserialize, Debug)]
 pub struct DocumentSnapshot {
+    pub format_version_major: u16,
+    pub format_version_minor: u16,
     pub canvas_elements: Vec<canvas::CanvasElement>,
 }

src/main.rs

@@ -187,7 +187,7 @@ impl AppDelegate<StilettoState> for Delegate {
                     data.canvas.set_from_snapshot(document_snapshot);
                     info!("Loaded file {}", file_info.path().display());
                 } else {
-                    warn!("didn't work: {:?}", res_snapshot.err());
+                    warn!("Error while loading {}: {:?}", file_info.path().display(), res_snapshot.err());
                 }
             }
             return Handled::Yes;

src/widget/canvas.rs

@@ -45,6 +45,8 @@ impl CanvasState {
 
     pub fn get_document_snapshot(&self) -> DocumentSnapshot {
         DocumentSnapshot {
+            format_version_major: 0,
+            format_version_minor: 1,
             canvas_elements: self
                 .versioned_canvas
                 .get()