Add support for did:tdw

[adrianmross]

Making an issue to track comments and suggestions for the implementation of did:tdw (spec). The did:tdw Trust DID Web is an enhancement to did:web, dare I call a predecessor, with the ability to chain/log updated versions of the DID Document for enhanced security, among many other things. This effort follows a discussion at IIW.

I have made a public fork to start an implementation of the did resolver module for this. Will make a PR once a significant portion is done and need review.

[TimoGlastra]

Sounds great, thanks @adrianmross!