feat(example): add example app and blog app with demos

examples/blog/app/controllers/posts_controller.rb

@@ -0,0 +1,24 @@
+class PostsController < Prism::Controller
+  layout :application
+
+  def index
+    render(:index, locals: { posts: Post.order(:created_at, :desc), notice: flash[:notice], errors: [] })
+  end
+
+  def show
+    render(:show, locals: { post: Post.find(params['id']) })
+  rescue Prism::Orm::RecordNotFound
+    halt(404, 'Post not found')
+  end
+
+  def create
+    post = Post.new(title: params['title'], body: params['body'])
+    if post.save
+      flash[:notice] = "Post ##{post.id} created"
+      redirect url_for(:posts)
+    else
+      status(422)
+      render(:index, locals: { posts: Post.order(:created_at, :desc), notice: nil, errors: post.errors.full_messages })
+    end
+  end
+end