add redcarpet markdown processor

* this is for rendering of Requirement descriptions
seed Requirement model from PCI Standards csv file
render requirement description using markdown

Failures:

  1) Manage proofs user views all requirements and proofs
     Failure/Error: visit signin_path
     ActionView::Template::Error:
       wrong argument type nil (expected String)
     # ./app/helpers/requirements_helper.rb:9:in `render'
     # ./app/helpers/requirements_helper.rb:9:in `markdown'
     # ./app/views/users/show.html.erb:24:in `block in
_app_views_users_show_html_erb___4593564265183360898_70352849857320'
     # ./app/views/users/show.html.erb:17:in
`_app_views_users_show_html_erb___4593564265183360898_70352849857320'
     # ./spec/features/manage_requirements_spec.rb:24:in `block (2
levels) in <top (required)>'

  2) Manage proofs user adds a new proof image
     Failure/Error: visit signin_path
     ActionView::Template::Error:
       wrong argument type nil (expected String)
     # ./app/helpers/requirements_helper.rb:9:in `render'
     # ./app/helpers/requirements_helper.rb:9:in `markdown'
     # ./app/views/users/show.html.erb:24:in `block in
_app_views_users_show_html_erb___4593564265183360898_70352849857320'
     # ./app/views/users/show.html.erb:17:in
`_app_views_users_show_html_erb___4593564265183360898_70352849857320'
     # ./spec/features/manage_requirements_spec.rb:35:in `block (2
levels) in <top (required)>'

  3) View the homepage guest sees requirements
     Failure/Error: visit root_path
     ActionView::Template::Error:
       wrong argument type nil (expected String)
     # ./app/helpers/requirements_helper.rb:9:in `render'
     # ./app/helpers/requirements_helper.rb:9:in `markdown'
     # ./app/views/requirements/index.html.erb:52:in `block in
_app_views_requirements_index_html_erb__638669791127906516_7035284431356
0'
     # ./app/views/requirements/index.html.erb:45:in
`_app_views_requirements_index_html_erb__638669791127906516_703528443135
60'
     # ./app/controllers/requirements_controller.rb:7:in `index'
     # ./spec/features/view_homepage_spec.rb:10:in `block (2 levels) in
<top (required)>'

Finished in 0.34184 seconds
5 examples, 3 failures, 2 pending

Failed examples:

rspec ./spec/features/manage_requirements_spec.rb:22 # Manage proofs
user views all requirements and proofs
rspec ./spec/features/manage_requirements_spec.rb:34 # Manage proofs
user adds a new proof image
rspec ./spec/features/view_homepage_spec.rb:6 # View the homepage guest
sees requirements