@spec help(responder :: t(), cmdprefix :: String.t()) :: [
  Polyjuice.Client.MsgBuilder.MsgData.t()
]

Get the general help for the responder.

A prefix will be passed; commands should be prefixed by the given prefix in the help text. It should return an array of items that implement the Polyjuice.Client.MsgBuilder.MsgData protocol; each item will be a separate line in the output for the help command.

@spec help(responder :: t(), cmdprefix :: String.t(), command :: list()) ::
  Polyjuice.Client.MsgBuilder.MsgData.t() | nil

Get the help text for a specific command.

A prefix will be passed; the command should be prefixed by the given prefix in the help text. If the responder implements the given command, it should return detailed help for the command. Otherwise, it should return nil. The command may have multiple components, and so is given as a list.