Implement user registration feature

* Add users/new action and view
* Add users/create action
* Add link to sign up in sign in page

spec/views/sessions/new.html.haml_spec.rb

@@ -23,4 +23,9 @@ describe 'sessions/new.html.haml' do
     rendered.should \
       have_selector('label[for=session_password]', :text => 'Password')
   end
+
+  it 'renders a link to the sign in page' do
+    render
+    rendered.should have_selector("a[href='#{new_user_path}']", :text => 'Sign up')
+  end
 end

spec/views/users/new.html.haml_spec.rb

@@ -0,0 +1,48 @@
+require 'spec_helper'
+
+describe 'users/new.html.haml' do
+  let(:user) do
+    mock_model('User').as_new_record.as_null_object
+  end
+
+  before do
+    assign :user, user
+  end
+
+  it 'renders a form to sign up' do
+    render
+    rendered.should have_selector("form[method=post][action='#{users_path}']")
+    rendered.should have_selector('input[type=submit]')
+  end
+
+  it 'renders a text field with a label for the mail address' do
+    render
+    rendered.should have_selector(
+      "input[type=text][name='user[email]']"
+    )
+    rendered.should have_selector(
+      'label[for=user_email]', :text => 'Email'
+    )
+  end
+
+  it 'renders a password field with a label for the password' do
+    render
+    rendered.should have_selector(
+      "input[type=password][name='user[password]']"
+    )
+    rendered.should have_selector(
+      'label[for=user_password]', :text => 'Password'
+    )
+  end
+
+  it 'renders a password field with a label for the password confirmation' do
+    render
+    rendered.should have_selector(
+      "input[type=password][name='user[password_confirmation]']"
+    )
+    rendered.should have_selector(
+      'label[for=user_password_confirmation]',
+      :text => 'Password confirmation'
+    )
+  end
+end