Image-diff

- Can now be run using `python -m image_diff` - thanks, [SuperSonicHub1](https://github.com/SuperSonicHub1). [#5](https://github.com/simonw/image-diff/pull/5)

- Fixed bug where `image-diff compile` command produced images using the incorrect orientation. [3](https://github.com/simonw/image-diff/issues/3)

- `image-diff count one.jpg two.jpg` command, to count the number of pixels different between two images. [1](https://github.com/simonw/image-diff/issues/1)
- `image-diff compile image.json -o output.png` command for compiling a simple JSON definition into an image file - useful for testing. [2](https://github.com/simonw/image-diff/issues/2)

- Initial release: `image-diff diff first.jpg second.jpg -o output.png` generates an image representing the difference between two other images.