Add autoload cookies each commands instead of require form with autoload cookie

This commit ensures that users who have installed `prosjekt` from [MELPA](http://melpa.milkbox.net/) will be able to use the code with lazy loading. For information about this fix, See [Packaging-Basics](http://www.gnu.org/software/emacs/manual/html_node/elisp/Packaging-Basics.html).