v0.13.0

Changed

• The Constitution agent reviews amendments as amendments. A diff that
  changes the constitution file itself is reviewed for rules that contradict
  each other or the code, not against the text it replaces, which it can
  only ever contradict. crunchtools/petit#77 and #78 each drew CRITICAL
  findings for changing the rule they were changing. Other files in the
  same diff are still judged by the base branch's constitution, so a PR
  still cannot relax a rule and use the relaxation at once. The agent is
  also told it does not know today's date, which made it flag same-day
  Amended: lines as stale.