Add FSM and related tool plumbing (Fix #54) (#62)

- Added FSM trait
- Added FSM to select and ellipse tools
- Moved circle stamping code to ellipse tool

core/editor/src/lib.rs

@@ -48,6 +48,6 @@ impl Editor {
 	}
 
 	pub fn handle_event(&mut self, event: events::Event) -> Result<(), EditorError> {
-		self.dispatcher.handle_event(&mut self.state, event)
+		self.dispatcher.handle_event(&mut self.state, &event)
 	}
 }