Parameterized type for `Algae.Maybe`

[neysofu]

Hi!

I think it would be useful to have a parameterized type for optional entities, e.g.

@spec f(Algae.Maybe.t(String.t())) :: any
def f(opt_name) do
  # ...
end

We could simply add a @type t(x) :: ... to Algae.Maybe, but ideally defdata would take care of it. Is it possible?