3.0.0-alpha055

Allow to reference git repositories - http://fsprojects.github.io/Paket/git-dependencies.html
Allow to run build commands on git repositories - http://fsprojects.github.io/Paket/git-dependencies.html#Running-a-build-in-git-repositories
Allow to use git repositories as NuGet source - http://fsprojects.github.io/Paket/git-dependencies.html#Using-Git-repositories-as-NuGet-source
Garbage collection in packages folder - #1491