Add helm-backup

Helm-backup try to simplify backup storing and management on emacs. This library permit to store every change made on files in a dedicated folder using git and to retrieve easily those changes using helm. At the moment it doesn't work for windows. 

I'm the author/maintainer.

Repo: https://github.com/antham/helm-backup

I think it's package.el compatible, but I'm not sure, is it adding autoload statement at the right place ?