Add SCP_OPTS and SFTP_OPTS

Use default awk on most images, add debian:latest and ubuntu:latest

Bugfixes for json_awk and nslookup

Recent versions of gawk have upgraded the regex processing with l10n
based character classes. Replace use of these so other versions of awk
can be used.

Debian dnsutils 1:9.11.5.P4+dfsg-5.1 errors on -debug=1

Dnsutils version 1:9.10.3.dfsg.P4-12.3+deb9u4 and version 1:9.2.1-2.woody.2
(from 2003) accept both -debug=1 and -debug so I've changed this globally.

Fix epoch_date for busybox and json_awk for gawk v5

Show error and exit if awk too old for ACMEv2

Improve tests

Implement testing using BATS

Use urlbase64_decode instead of base64 -d

ACMEv2 during testing

Ignore directories when using `getssl -a` if they don't contain a config file

Add Webdav over HTTPS (davs) file transfer method using curl

Create dns_freedns.sh

Add support for CloudDNS

markdownlint changes to all .md files

Fix more than 10 domains

Rename getssl.test host to ubuntu16.getssl.test