Added
- The `response_code` option for `response()` and `json_response()`.
- The `sendgrid api key` Configuration directive for sending e-mail
using the SendGrid API.
Changed
- A `question` with a Continue button that sets a variable to `True`,
or a `review` screen with a Continue button instead of a Resume
button, can be indicated with `continue button field` instead of
`field`.