GitLab

 - metadata is specific to web, move it there
 - create Web_serializable, and also move randomness there
 - metadata is not optional (but its components can be)
 - rename user_type into user_domain
 - serializable version of ACLs

It is used for ballots as well as records...

A record (i.e. who voted, when and with which credential in the
context of the web server) is a notion that does not exist in the
cryptographic protocol and does not really make sense in the context
of the command-line tool.

By the way, we add the notion of receipt which, in the context of the
web server, is the ballot hash computed by the server.

Bonus: when a ballot is accepted, we compute its hash only once.

The credential is taken from the file given to --privkey (if any).

 - make "decrypt" a subcommand instead of an option
 - show help when called with no argument
 - split default action into "verify" and "finalize" subcommands

This should be reverted once the booth is adapted...

 * drop ELECTION_PARAMS signature
 * parameters are no longer implicit in ELECTION signature
 * redesign WEB_ELECTION signature

 * remove unneeded commitments
 * s/commitment/public_key/g in signature