Ajout des sections dans les exemples
[WIP] Application des discussions sur les packages

Discussions :

- http://github.com/patacrep/songbook-core/pull/32#issuecomment-43410215
- http://github.com/patacrep/songbook-core/commit/ba15ad1093fd28103521feed923b764102be8923#commitcomment-6359206