Fix issues in presence signatures (no tests SHA-512), typos, update
gnupg.py to a recent version, fix the completion, and display the
messages we send properly

(and fuck the scoping of python closures)

Join the fake room first, then send the message to nickserv, then join
initial rooms.

Also add two commands and one option.

Allow -1 as a value for optional arguments in the args parser to collect an unspecified number of items

incomplete, but will help catch obvious wrong behaviors if we change
anything in the completions.

(e.g. during a completion, the input might scroll due to the length of
the completed item, and not go back to its original state without this
change)

I wish I didn’t have to do such ugly things to get a close-to-decent
interop with legacy OTR plugins that insert awful HTML4 stuff inside
messages that do not need it.

- Add two new options, keyfile and certfile, which must be both set for
  the auth to work.
- if both are set, then poezio doesn’t force-prompt a password if there
  is none specified
- add /cert_add, /cert_fetch, /cert_disable, /cert_revoke and /certs
  commands.
- add a page of documentation on the process

through overloading the class variable default_config.
also fix a bug that would add meaningless sections to plugin
configurations.