int64_le
64 bit low endian signed integer
iex> defmodule Struct do
...> use BinStruct
...> field :value, :int64_le
...> end
...>
...> Struct.new(value: -1)
...> |> Struct.dump_binary()
...> |> Struct.parse()
...> |> then(fn {:ok, struct, _rest } -> struct end)
...> |> Struct.decode()
%{ value: -1 }