- Removal of RFC2136_ZONE from help text
- Query nameserver directly to find zone we have to update
- During insert, make sure the new record is the ONLY challence.
(I had a few panics, hence 3 challences left. Not good.)
Add a new environment variable RFC2136_TSIG_ALGORITHM that accepts the
TSIG algorithm pseudo-domain name. Let it default to
"hmac-md5.sig-alg.reg.int." if unset.
* new ChallengeProvider with Present and CleanUp methods
* new Challenge type describing `http-01`, `tls-sni-01`, `dns-01`
* new client.SetChallengeProvider to support custom implementations
