Add markdown support

Markdown support added for episode synopsis and review body.  Test added for episode synopsis markdown support.  Review body markdown support test dependent on review test suite.
You should be able to add `.html_safe` into the helper

```ruby
module ApplicationHelper
  def render_markdown(markdown)
    extensions = { hard_wrap: true }
    renderer = Redcarpet::Markdown.new(Redcarpet::Render::HTML, extensions)
    renderer.render(markdown).html_safe
  end
end
```