2721d64989 chainparams: Add achow101 DNS seeder (Ava Chow)
Pull request description:
I wrote a [DNS seeder](https://github.com/achow101/dnsseedrs) and have been running it for the past 2 months now. I believe it is ready/good enough to be used as an additional DNS seeder for all of our supported public networks.
ACKs for top commit:
laanwj:
ACK 2721d64989
1440000bytes:
~~reACK 2721d64989~~
mzumsande:
ACK 2721d64989
willcl-ark:
reACK 2721d64989
Tree-SHA512: 857a6cf7dd33962f0008a89db4d6b57d3c6aa622704cdcca6ab710babeead3a2970d9a6fa190949c7bbf7cb7d006e814d6314be3d8c8180eed29013c7c1ac7e1