publish command receive the draft path

This change a little bit the publish command.

I think it make sense for the `post` and `draft` command to receive the name (title) of the post.. that way you can create the file in the corresponding folder.

But for `publish` it makes more sense to pass the entire path of the draft you want to publish. This is because this way you can use the autocomplete `jekyll publish _drafts/my-draft-post.md`. I think is easier.
can you validate that this exists?