Add JSONIFY_MIMETYPE configuration variable

[sloria]

It is often useful to be able to return a vendor media type for JSON responses. For example, JSON API requires that all responses have the Content-Type: applications/vnd.api+json header.

[jeffwidman]

LGTM

[untitaker]

LGTM, but the changelog entry is now for the wrong version.

[sloria]

OK, I've rebased with the latest master and put the changelog entry in the 1.0 section.

[davidism]

I'm currently implementing a new "JSON provider" interface for customizing how an app handles JSON. As part of that, I'm deprecating the app.config["JSONIFY_MIMETYPE"] parameter in favor of setting app.json.mimetype (along with some other config that makes more sense as provider setup).

However, reviewing this I'm not clear that setting the mimetype unconditionally is correct. The JSON API mimetype seems to be specifically for responses related to its own metadata and introspection, not to the actual API responses. It makes much more sense to me to set the content type for the specific responses that need it:

response = jsonify(data)
response.mimetype = "application/vnd.api+json"
return response

Am I missing something here or can I remove the configuration entirely? Note that it would still be possible to change the default using a custom provider:

class VndProvider(DefaultJSONProvider):
    def response(self, *args, **kwargs):
        response = super().response(*args, **kwargs)
        response.mimetype = "application/vnd.cool-api.v1+json"
        return response

app.json = VndProvider(app)