Implement an Authenticator which can fulfill a dns-01 challenge using
the DNS Made Easy API. Applicable only for domains using DNS Made Easy.
Testing Done:
* `tox -e py27`
* `tox -e lint`
* Manual testing:
(`http://api.sandbox.dnsmadeeasy.com/V2.0` used as the
`api_endpoint` for all manual testing)
* Used `certbot certonly --dns-dnsmadeeasy -d`, specifying a
credentials file as a command line argument. Verified that a
certificate was successfully obtained without user interaction.
* Negative testing:
* Path to non-existent credentials file.
* Credentials file with unsafe permissions (644).
* Path to credentials file with an invalid API key.
* Path to credentials file with a malformed API key.
* Path to credentials file with an invalid Secret key.
* Path to credentials file with a malformed Secret key.
* Domain name not registered to DNS Made Easy account.
