Add helper generator feature

Author: vivekmiyani

features/generator_specs/helper_specs.feature

@@ -0,0 +1,25 @@
+Feature: Helper generator spec
+
+    Scenario: Helper generator
+        When I run `bundle exec rails generate helper posts`
+        Then the features should pass
+        Then the output should contain:
+          """
+                create  app/helpers/posts_helper.rb
+                invoke  rspec
+                create    spec/helpers/posts_helper_spec.rb
+          """
+
+    Scenario: Helper generator with customized `default-path`
+        Given a file named ".rspec" with:
+          """
+          --default-path behaviour
+          """
+        And I run `bundle exec rails generate helper posts`
+        Then the features should pass
+        Then the output should contain:
+          """
+                create  app/helpers/posts_helper.rb
+                invoke  rspec
+                create    behaviour/helpers/posts_helper_spec.rb
+          """