Infix variant of Monoid.append

Example

iex> import Witchcraft.Monoid
...> defimpl Witchcraft.Monoid, for: Integer do
...>   def identity(_), do: 0
...>   def append(a, b), do: a + b
...> end
iex> 1 |> append(4) |> append(2) |> append(10)
17

iex> 1 <|> 4 <|> 2 <|> 10
17

iex> import Witchcraft.Monoid
iex> 1 |> append(4) |> append(2) |> append(10)
17

iex> [42, 43] <|> [44] <|> [45, 46] <|> [47]
[42, 43, 44, 45, 46, 47]