Certbot-dns-duckdns

Fixes:

- hyphens in the domain work now 10 11 (special thanks to durnezj)
- added support for arbitrary number of additional subdomains

Changes:

- updated Docker image to allow more flexible usage, see the readme for more information

Other:
- removed unused code and dependency

Fixes:
- fixed missing default value for PROPAGATION_SECONDS value in docker image 6
- fixed an issue with the autorenew in the docker image 8

New:
- prebuild images for multiple architecture are now available on [Ducker Hub](https://hub.docker.com/r/infinityofspace/certbot_dns_duckdns) #5

Changes:
- version requirement of certbot was raised to 1.7.0 to fix issues with older and unsupported certbot versions

Fixes:
- fixed an issue with old certbot versions 2

New:
- added docker support

- fixed an issue with wildcard domains (1)