Refactor i18n structure, remove layouts, add slides

Yep, this commit is too big big I didn't want to take the trouble of splitting
it now.

- _config.yml translation keys are now simetrical on the entitiy: articles,
pastebins, tils, slides, etc.;
- _posts were moved to _articles: the _posts collection had special treatment in
Jekyll which I wanted to avoid;
- the filtering of entries for the Atom feed is now done inside the
_includes/feed.atom file instead of every feed file;
- all entities are now dealt with using the pluralized name: articles,
pastebins, tils, slides. No more inconsistencies on the key names, they now
should only make sense as the translation value on the dictionary;
- add base reveal.js infrastruture, with Jekyll generating the listing page and
nothing else.

1 files changed, 1 insertions, 1 deletions

diff --git a/about.md b/about.md
index d203f15..dd5b4c3 100644
--- a/about.md
+++ b/about.md
@@ -26,4 +26,4 @@ LaTeX sources into songbooks.
 
 ## Other things
 
-[Pastebins listing](./pastebins.html).
+[Pastebins listing]({% link pastebins.en.md %}).