Returns a Timbre appender that sends gelf messages to a remote host. Params:
`gelf-server` - IP address or hostname string of the remote logging server
`port`        - TCP or UDP port on which the server listens
`protocol`    - e/o #{:tcp :udp}, defaults to :udp

Returns a new GelfTransport object, capable of sending a GelfMessage to a
remote server. Params:
  `host`     - IP address or hostname string of the remote logging server
  `port`     - TCP or UDP port on which the server listens
  `protocol` - e/o #{:tcp :udp}