Unnest routes

[jrhorn424]

https://github.com/ga-wdi-boston/rails-api-bdd/pull/18#discussion_r101407939

[danman01]

Things to update if we do un nest these routes:

• README.md: "Our first step will be to create feature tests to account for these new requirements. Create a new file: spec/requests/article_comments_spec.rb." -> "Our first step will be to create feature tests to account for these new requirements. Create a new file: spec/requests/comments_spec.rb."

• Request specs spec/requests/article_comments_spec.rb -> Move content to comments_spec.rb (GET and POST requests)

• Routing specs -> article_comments_spec.rb content to comments_spec.rb

• Comments controller specs -> move content to comments_controller_specs.rb

• Comments controller -> verify routes are working as expected without use nested routes. Since we're just rendering json it should be fine.