Ggb

- Add CLI support.

- Resolve error in reading YUV color space.
- Improve compatibility ``skimage`` format for ``GGBImage``.
- Add some documentation and testing utilities.

- `GGBImage` can not be called directly from `ggb` module.
- Add `ggb.testing` module.
- Move `ggb.utils.test` module to `ggb.testing.base` module.
- Add `get_image_from_url` function in the `ggb.testing.base` module.
- Add `process` method in the `ggb.backend` module.
- Rewrite `ggb.ggb` module.
- Add `ComputerVisionLibraryError` exception in the `ggb.utils.error` module.
- Tidying up code for documentation.

- Add testing utilities
- Simplify syntax for `scikit-image`
- Tidying up code in accordance with PEP8

- Support OpenCV, PIL (Pillow), and scikit-image (skimage) format.
- First public release version.