Ajout de sphinx-spelling de façon à pouvoir vérifier automatiquement l'orthographe du syllabus à chaque commit.

Suppression du texte concernant les QCM.

use exit_on_error consistently in fork-pipe.c

add qbf for fifth week

add qbf for fourth week

update qbf-3: add gcc option for deterministic result

add qbf-s3 and fix formatting

update qbf for second week

add exercises and fix layout for second week

fix failed travis build due to missing reference

Fixes ex s1

Reason: recent versions of gcc won't complain for the return value of the
main() function, even with -Wall.

Exercices S1: ajout d'une question de bilan final

Correction orthographe et erreur Systèmes de fichiers

Modification code question 8 (main return void)

Glossaire 

Fix typos partie S2