Disallow naming an article 'new', or any already used slug

Fix #64

Also fixes a lot of potential bug with articles having the same slugs, but not in the same blog

src/routes/blogs.rs

@@ -75,7 +75,7 @@ fn create(conn: DbConn, data: Form<NewBlogForm>, user: User) -> Redirect {
             author_id: user.id,
             is_owner: true
         });
-        
+
         Redirect::to(format!("/~/{}/", slug))
     }
 }