FindPkgs looks for packages matching the inputs inside the database.
It returns a map that maps the package name input to the packages found for it.
It also returns a slice that contains the names of all packages that were not found.
Pull pulls the provided repositories. If a repo doesn't exist, it will be cloned
and its packages will be written to the DB. If it does exist, it will be pulled.
In this case, only changed packages will be processed.