adding pre-existing flip/rotation functionalities to the image menu, and setting fixed options for vertical/horizontal flip and left/right 90 degree rotation

README.md

@@ -20,13 +20,13 @@ Image menu
 - Select
     - [x] Rectangular selection
     - [x] Free-form selection (Lasso)
-    - [ ] Polygon selection
+    - [x] Polygon selection
     - [x] Crop
     - [x] Resize
-- [ ] Rotate right 90 degrees
-- [ ] Rotate Left 90 degrees
-- [ ] Flip vertical
-- [ ] Flip horizontal 
+- [x] Rotate right 90 degrees
+- [x] Rotate Left 90 degrees
+- [x] Flip vertical
+- [x] Flip horizontal 
 
 Tools menu
 - [ ] Zoom (Zoom In, Zoom Out)