Dnsrobocert

Added
* Continuous integration/deployment is now handled by CircleCI to allow more advanced strategies and faster builds
* Add and configure Circus, an alternative to Supervisor, compatible with Python 3, with better control over environment variables propagation, and network sockets supervision (not used yet here)

Changed
* Update base image to Alpine 3.8
* Update Lexicon to 2.7.3
* Update Certbot to 0.27.1

Removed
* Docker Hub "Automated build" is disabled in favor of CircleCI
* Remove Supervisor and its configuration (in favor of Circus)

Added
* `LEXICON_OPTIONS` was added to the cleanup script 29

Changed
* Avoid to mark `domains.conf` as edited on each watch loop

Changed
* Correct `domains.conf` parsing for particular cases (wildcard domains on the last line of the file)

Changed
* Upgrade Certbot to 0.26.1
* Upgrade Lexicon to 2.7.0, with extended security support for Subreg
* Correct certificate revocation for some formatting for `domains.conf`

Changed
* Upgrade Certbot to 0.26.0
* Upgrade Lexicon to 2.6.0, including new DNS providers: ExoScale, Zeit, and Google Cloud DNS