Support multiple errors

[cognivore]

Why?

errors =
  [cy, dy]
  |> Enum.filter(&Result.is_err?/1)

case errors do
  [] ->
    conn
    |> put_resp_header("X-Nonsense-Auth-Chal", cy |> extract)
    |> send_resp(200, dy |> extract |> Jason.encode!())

  _ ->
    conn
    |> send_resp(403, errors |> Jason.encode!() |> to(%Err{}))
end

This sucks, because the consumers may expect a well-formed Err of type

@type err(e_t) :: %{
        required(:__struct__) => Elixir.Uptight.Result.Err,
        required(:err) => %{
          required(:exception) => e_t,
          required(:stacktrace) => list(any()),
          required(:__struct__) => Elixir.Uptight.Trace
        }
      }

But instead they gets something of type %{ ... required(:err) => list(err(any())}.

How?

• Create a new wrapper type Errs, which wraps such list
• Define all the instances for it (can we derive them from a list?!)
• Replace Applicative call to to(%Errs{}).
• Demo handling Errs as well as Err from typescript.