fixed `core/Vector`: `translate` returns `this`
improved `shapes`: minor fixes & tweaks

- renamed internal references
- code optimizations -> smaller `/dist` files
`core/Matrix3`: `applyToVector` -> `translation`

- minor tweaks -> smaller `/dist` files
`core/Canvas`: `tr` -> `tl`
`core`: let `Rectangle` inherit from `Polygon`

DRY -> smaller `/dist` files
`core`: let `Square` inherit from `Rectangle`

DRY -> smaller `/dist` files
`util`: added `Group` class

`Group` is a utility class to call methods of many objects
simultaneously. It helps your organizing your node tree.