0.26

• Update and improve security model documentation.
• Streamline conntrack rules, move them to top-level chains to avoid
  duplication.
• Narrow focus of input iptables chain so that it only applies to
  Calico-handled traffic.
• Provide warning log when attempting to use Neutron networks that are not of
  type 'local' or 'flat' with Calico.
• Handle invalid JSON in IPAM key in etcd.
• Move all log rotation into logrotate and out of Felix, to prevent conflicts.
• Change log rotation strategy for logrotate to not rotate small log files.
• Delay starting the Neutron resynchronization thread until after all the
  necessary state has been configured, to avoid race conditions.
• Prevent systemd restarting Felix when it is killed by administrators.