Multi-line doc string argument in a step.
Build a DocString struct.
@type t() :: %Cucumberex.DocString{ content: String.t(), content_type: String.t() | nil, delimiter: String.t() }
iex> Cucumberex.DocString.new("hello").content "hello" iex> Cucumberex.DocString.new("x", "text/plain").content_type "text/plain"