The review request resource now has a 'close_description' field that

will be set to the close description text, if provided and if closed.

This makes it easier to see the status of a review request without

digging into other resources.
This also deprecates the 'description' field when closing a review

request through the API. The new argument is 'close_description', which

matches the returned value and doesn't conflict with the field.

Unit tests pass.
Verified the field through the API.
Profiled and saw that only 1 new query was added (for the changedescs

prefetch).