Add Aurora DNS API

[JaZo]

This PR adds support for the Aurora DNS API offered by the Dutch cloud provider PCextreme B.V.

Documentation: https://github.com/acmesh-official/acme.sh/wiki/dnsapi#131-using-the-aurora-api
Issue: #3459
Latest actions run: https://github.com/JaZo/acme.sh/actions/runs/753125822

[Neilpang]

BTW, please fix your CI checks:
https://github.com/JaZo/acme.sh/actions/runs/692884497

It's not passing.

[JaZo]

@Neilpang I've re-ran the action several times, but every time it fails at a different point. The logs also don't give me a clue of what went wrong. One time it got through and even reached the FreeBSD job and then it failed on some SSH and Rsync issues. Do you have a direction I should look? Those issues don't seem to be related to my new API implementation, but maybe I'm overlooking something?

[Neilpang]

please set a larger TEST_DNS_SLEEP value.

https://github.com/acmesh-official/acme.sh/wiki/DNS-API-Test

[JaZo]

@Neilpang My implementation had some issues on OS X, but I managed to fix those. Build is successfull now, so it's ready for review!

N.B. shfmt job is failing, but that's caused by a different DNS API.