Distinguish between unused let variables and function parameters

[tad-lispy]

Personally I find this:

init flags =
    ( 0, Cmd.none )

more readable than this:

init _ =
    ( 0, Cmd.none )

This is of course a matter of opinion. The problem is that if I disable UnusedVariables, then this is also accepted:

init flags =
    let
        wat = "unused"
    in
    ( 0, Cmd.none )

Which is definitely a mistake. So maybe there should be two checks: UnusedLetVariable and UnusedFunctionParameter?