Speaking frankly, I felt that the peerdid library was a bit overly
complicated. On top of that, peerdid is not up to date with the
corrections proposed in this PR to the did:peer method specification:

decentralized-identity/peer-did-method-spec#62

did-peer-2 is a minimal implementation of did:peer:2 and did:peer:3.
It is up to date with the above PR. The corrections to the spec and the
library lend themselves to a simpler implementation of the did:peer:2
and did:peer:3 resolvers. This refactor supports work to add did:peer:2
support to OOB + DID Exchange.

New in this PR is a cleanup mechanism for the did:peer:3 to did:peer:2
mapping records. When a connection is deleted, we check whether there
are any potential mappings to remove.

Signed-off-by: Daniel Bluhm <dbluhm@pm.me>

Signed-off-by: Stephen Curran <swcurran@gmail.com>

Signed-off-by: Stephen Curran <swcurran@gmail.com>