New bindings

- add support for ``erode`` based on ``dilate`` implementation
- add support for ``GaussianBlur`` with ``ksize`` optional argument
- add support for ``arcLength`` in contours
- add support for ``approxPolyDP`` in contours
- add support for ``isConvex`` in contours
- add support for ``boundingBox`` in contours --> returns an (x, y, width, height) object

Maybe other to follow as need arise :)