remove config frontends from engine
start encapsulating config
rearrange; conflate rekeying options
split (external) config for client/server
peer_hame handled separately
port lwt
fix feedback
http_client: don't require secure rekeying

:)
port mirage
XXX_exn
fix lwt
fix feedback
Merge pull request #105 from mirleft/validated-config

Encapsulated configs