Structure that holds all the elements of an individual function
t() :: %ExDoc.FunctionNode{annotations: list, arity: non_neg_integer, defaults: non_neg_integer, doc: String.t, doc_line: non_neg_integer, id: nil | String.t, name: nil | String.t, signature: nil | String.t, source_path: nil | String.t, source_url: nil | String.t, specs: list, type: nil | String.t}