Add support for yang-data+xml and yang-data+json

[mjethanandani]

No description provided.

[kwatsen]

I sent a message to the list asking for a clarification on the correctness of using "yang-data"

[kwatsen]

I did send a message to the list, and Alex replied, effectively, that the current PR is okay. That said, he also wrote;

That said, if the authors really do want to add HTTPS-Notif support for legacy (RFC5277), then the way I would do it is adding a new Section after Section 4, stating that this spec can also be used with legacy notifications as defined in RFC5277. In this section, I would add a paragraph stating how this mechanism is used (using application/xml as media type when sending Notifications, and how are the capabilities advertised in a RFC5277 environment).

Which I think should be done.