Add image_optim to gh-pages

Images optimised using [image_optim](toy/image_optim) v0.19 with following commands:
```sh
image_optim -r images/image_optim --jpegtran-jpegrescan=true
image_optim -r images/image_optim-lossy --jpegtran-jpegrescan=true --allow-lossy
```
Full disclosure: I am the main developer of image_optim :)