Add convenience method to access entities and resources

ecs/src/world.rs

@@ -95,6 +95,18 @@ impl World {
         self.entities.values()
     }
 
+    pub fn entity_resources(
+        &mut self,
+        entity: Entity,
+    ) -> Result<(&mut EntityObject, &mut Resources)> {
+        Ok((
+            // actually safe:
+            // entity_mut only accesses entity map
+            unsafe { remove_life_time_mut(self.entity_mut(entity)?) },
+            &mut self.resources,
+        ))
+    }
+
     pub fn entity(
         &self,
         entity: Entity,