New Features

Added /v1/info API endpoint gives information about the doomsday server version and configured auth method.
Added tlsclient backend. Configure this backend with a list of hosts to check, and it connects over tcp, initiates a handshake, and returns the served TLS certificate.
Added support for multiple backends to be queried from a doomsday server.
Added a -d flag to the CLI target command, which deletes the named target.
Session timeout length and refresh-on-use for userpass auth is now configurable in the server manifest.

Enhancements

The doomsday CLI now handles attempting to login to a doomsday server no auth more gracefully.
The doomsday server now defaults to listening on port 8111 if server.port is not given in the manifest and no PORT environment variable is found.
The CLI now does basic URL validation when adding a target.
The CLI now defaults the port of a target to 8111 if not specified.

The backend manifest key is now called backends. Also, it's a list now. Because multiple backends.
The backend.config key was changed to properties. Also, many of the properties for a backend that were above this level were moved into properties (e.g. address and insecure_skip_verify) because they were no longer universal across all backends.
The server.auth.config key was changed to server.auth.properties for consistency with backends.
Several keys (which are now under properties hashes) have changed types (and therefore values). Originally, the code only allowed for values to be strings, which wasn't great. Now things can be numbers and bools, and so several properties have changed to benefit.

The new manifest schema can be found at docs/ddayconfig.yml