Split document into individual sub-documents

[juberti]

The document explains how it replaces several previous specs:

In this regard, RIPP replaces the usage of SIP, SDP offer/answer [RFC3264] and RTP [RFC3550] for this particular use case.

I think each of these will require specific work to handle the general case and I tend to think we should split the document accordingly, perhaps with an overview doc to knit them all together.

Specifically, I think the encapsulation of media over QUIC will be complex and will definitely want to live as its own doc.

[fluffy]

+1

I would also like to get the goals and pro/cons for all this very separate from the key technical specs. I would like them to be as brief as possible.