Stop the snow animation when scroll in higher than the header

CPU and mobiles battery will not melt this december \o/
Merge pull request #28 from damienalexandre/fix-snow

Stop the snow animation when scroll in higher than the header
Merge pull request #26 from j0k3r/migrate_to_sf2_3

Add RSS feed to the Advent calendar
[Avent]Ajout article prez AFSY
Enable align-left image in article
Fix Mise en page image