Use elm-units for durations

[MartinSStewart]

Hi, one suggestion I have is to use elm-units instead or having your own API for dealing with durations. Then you can just have after : Duration -> msg -> Cmd msg, sequence : List ( Duration, msg ) -> Cmd msg, and sequenceIf : Bool -> List ( Duration, msg ) -> Cmd msg and anyone familiar with elm-units won't need to relearn how to specify what time units they want or do extra conversions if they are already using elm-units for other stuff.

[andrewMacmurray]

Thanks @MartinSStewart, there was a suggestion on this thread https://discourse.elm-lang.org/t/elm-delay-4-0-0/7031/3 that the duration functions read a bit awkwardly and that withUnit could be more general and could accommodate things like elm-unit in a nicer way.

elm-units definitely has a nice api! I think given that elm-delay is so tiny it would be a shame to force others to use this as a peer dependency, particularly if their use case is very simple