REPO mode to retrieve application recipe

Right now when you want to install an application in libre.sh 1.1 you need to specify the full repo like :

libre provision -a lab.libreho.st/libre.sh/compose/prestashop etc...

Which should stay the default mode.

However it would be great to have a setting "REPO" for the root of the git repo like

REPO=lab.libreho.st/libre.sh/compose/

So we could just call

libre provision -a prestashop