TODO

- We have forked babeld for several changes. We'd like all our patches to be
  merged upstream. See https://lab.nexedi.com/nexedi/babeld

- Filter non-routable IPs. Add an option not to do it.

- More runtime configuration changes (i.e. without complete restart).

- Several subprocesses like babeld are started at the beginning and never
  watched, because they should never exit. Their management must be moved to
  the main loop, to restart them in case of failure or configuration change.

- Put more information in the token mail (registry), such as:

  - the ip address of the network being built
  - the creator of the network ( add option in registry ? )

- registry: add '--home PATH' command line option so that / display an HTML
  page from PATH (use new str.format for templating)

- Better UI to revoke certificates, for example with a HTML form.
  Currently, one have to forge the URL manually. Examples:
    wget -O /dev/null http://re6st.example.com/revoke?cn_or_serial=123
    wget -O /dev/null http://re6st.example.com/revoke?cn_or_serial=4/16