Use articles resource for routing

Change the routes configuration to use resources :articles instead of
specifying every single route for the Article resource one by one.

* Replace per action Article routes with resource in routes config
* Update the index view to use the link_to helper for each Article
* Update the ArticlesControllerTest to use article_path

Completes Rails Getting Started Guide:
* 7 CRUDit Where CRUDit Is Due
  * 7.2 Resourceful Routing

app/views/articles/index.html.erb

@@ -3,9 +3,7 @@
 <ul>
   <% @articles.each do |article| %>
     <li>
-      <a href="/articles/<%= article.id %>">
-        <%= article.title %>
-      </a>
+      <%= link_to article.title, article %>
     </li>
   <% end %>
 </ul>

config/routes.rb

@@ -1,6 +1,5 @@
 Rails.application.routes.draw do
   root "articles#index"
 
-  get "/articles", to: "articles#index"
-  get "/articles/:id", to: "articles#show"
+  resources :articles
 end

test/controllers/articles_controller_test.rb

@@ -13,7 +13,7 @@ def setup
   end
 
   test "should get show" do
-    get "/articles/#{@article.id}"
+    get article_url(@article)
     assert_response :success
     assert_select 'h1', @article.title
     assert_select 'p', @article.body