+ Link to 'by tag' and 'all articles' from the paginator in front page
~ article 'preview/excerpt' is being externalized into a file so it can
be referenced from the front paginator and the index page
~ moved mastodon js & css code to index.html (the only place where it should be useful)
+ activation of mastodon : 1st try
+ link on toots' images to open them
~ read speed fixed (was too optimistic)
~ minor fixes in articles
~ fixed : links can now be split on the next line (was not readable on mobile devices)
+ post's related posts with jekyll-tagging-related_posts but not activating it since it looks wrong
+ `rel="me"` for mastodon verification
~ about page updated
- removed unused `about.md` & `assets/index.html`
