• Configuring MDCAChallenges replaces any previous existing challenge configuration. It
  had been additive before which was not the intended behaviour. [@mkauf]
• Fixing order of ACME challenges used when nothing else configured. Code now behaves as
  documented for MDCAChallenges. Fixes #156. Thanks again to @mkauf for finding this.
• Added a script - inspired by curl https://github.com/curl - that collects contributors
  from the git commits and PRs. Adding a "Thanks" section with their names in the README.md.