Add install generator and support Rails 3 or 4

spec/generators/swagger_rails/install_generator_spec.rb

@@ -0,0 +1,20 @@
+require 'rails_helper'
+require 'generators/swagger_rails/install/install_generator'
+
+describe SwaggerRails::InstallGenerator do
+  include GeneratorSpec::TestCase
+  destination File.expand_path('../tmp', __FILE__)
+
+  before(:all) do
+    prepare_destination
+    run_generator
+  end
+
+  it 'creates a default swagger.json file' do
+    assert_file('config/swagger/v1/swagger.json')
+  end
+
+  it 'creates a swagger_rails initializer' do
+    assert_file('config/initializers/swagger_rails.rb')
+  end
+end