Add categories'management

[PetiPandaRou]

I would like to use categorization in order to blog on different subject.
For now, it's not possible to use them in articles.

[PetiPandaRou]

Starting working on it on my personal blog.
Still amelioration to be done (adding link to category page)

[aigarsdz]

As far as I know, category pages with Jekyll are complicated. The easiest option would be to use a plugin, but that's a problem if you want to host your blog on GitHub, because GitHub pages don't support plugins. Another option is to manually create a page for each category. I haven't tried either of these options myself. Maybe there are others. I'll look into it.