Remove codec

Delete all the varstruct codec stuff.
I originally figured that a cryptosystem needed a binary protocol.
If you can't handle binary, you can't handle crypto. That is what I thought.
This attitude was silly though, because I wasted a lot of time debugging the binary stuff.
Also, secure-scuttlebutt needs flexibility (because we went to flexible user messages), and that is much easier with json.

On this pr it's currently still using json-human-buffers, but I think i'll port all the signatures to use base64 too,
and then we can just use completely standard json.

Instead of hardcoreness, we want to design towards being easy to reimplement... only with multiple implementations can we be truly decentralized.