Add RSS feed

[soygul]

This is useful for posts: https://github.com/jekyll/jekyll-feed along with this to make it work with GitHub pages: https://dzhavat.github.io/2020/01/19/adding-an-rss-feed-to-github-pages.html

It supports collections that are not posts so all we need is dates on the old posts and some configuration.

[holdit]

Waiting for this.

[soygul]

quanticdev.com uses simple pages instead of jekyll posts. That's why this has been delayed for a while. I'm thinking of solving this with a pull-request to jekyll-feed plugin instead of modifying all pages on quanticdev.