Handle file downloads

[amacleay-cohere]

Is your feature request related to a problem? Please describe.
Sometimes, the response from an API we wish to use is some media type that can't easily be parsed into text, and I wish to receive it as a blob.

Describe the solution you'd like
Respond to format: binary in the response description and return a blob from useGet/useMutate

Describe alternatives you've considered
I can bypass restful-react processing by providing a type of */*, and I get back the raw Response object, thanks to #262, which is fine, although requires typescript hacking