Add the ability to set API info (title, description, license, terms and contact email)

I needed to have an API introduction and didn't see any way to do this, so I added it. Now you can say:

```ruby
add_swagger_documentation info: {
  title: 'api title here',
  description: 'a longer description of the api and use cases/etc here',
  contact: 'contact email',
  license: 'the name of the license',
  license_url: 'the url of the license',
  terms_of_service_url: 'the url of the api terms and conditions'
}
```