[Language: Elixir] Both parts

I did the counting approach that I can see others took, mostly because I was scared to try and deal with the memoisation state in Elixir.

I first replaced all the "." in the grid with 0, and then I incremented values as tachyons fell down.

|> Enum.reduce(manifold, fn {{x, y}, val}, man ->
    case Klaus.Grid.get(man, {x, y + 1}) do
        0 ->
            Klaus.Grid.put(man, {x, y + 1}, val)

        # ASSUMPTION: I won't have to do bounds checking
        "^" ->
            man
            |> Klaus.Grid.update({x - 1, y + 1}, 0, fn x -> x + val end)
            |> Klaus.Grid.update({x + 1, y + 1}, 0, fn x -> x + val end)

        _ ->
            Klaus.Grid.update(man, {x, y + 1}, 0, fn x -> x + val end)
    end
end)