Compact config representation

[willscott]

Probably worth revisiting the JSON file serialization used for talek.conf and talek.handle. In particular, the "public key as array of bytes" is probably better represented hex-encoded.

Ideally a handle would be serialized to a single line that was short enough to copy-paste. This compact representation could be (for example)
seed1.seed2.shared_secret.sequence_number