Some ideas and improvements

[Sohn123]

Hi there,
I used anatole for some time and was quite happy with it, but stumbled upon some things I'd like to change:

1. Use hugos preprocessing of images (docs) to serve responsive images on the portfolio site
2. Use postcss, purgecss and nanocss to remove unnecessary CSS and compress the rest (docs)
3. Use SVG favicons (article)
4. Add webmanifest and theme color meta tag
   I already implemented most of the features on my own fork of anatole on the prod branch, but I'm not 100% sure if these are desired features of the other anatole users. And some of the features would require configuration changes. I'd be happy to contribute some of them, if anyone else besides from me would like to have them.