* refactor: create log.Infof and log.Warnf
* refactor: review DNS providers.
- use one `http.Client` by provider instead of one client by request
- use the same receiver name `d` for all `DNSProvider`
- use `http.MethodXXX`
* refactor: logger init.
* Add NS1 DNS provider.
Integrates Lego with NS1 using their rest API.
It uses NS1's official Go package as client:
https://github.com/ns1/ns1-go
Signed-off-by: David Calavera <david.calavera@gmail.com>
* Add NS1 to the cli handlers.
Signed-off-by: David Calavera <david.calavera@gmail.com>
