Update for most recent Json API
style: modernize for Haskell style guide
Point to correct source directory
Turn default imports back on

The default imports are now:

    import Basics (..)
    import Maybe (Maybe(..))
    import Result (Result(..))
    import Signal (Signal)

Outside of Basics, the idea is that these types are so commonly used
that it makes sense to bring them into scope everywhere. Furthermore,
since it’s just types and type constructors, there will be no dumb name
collisions like Maybe.map vs List.map vs Result.map. You can bring in
an unqualified version of map depending on what you want to do in
particular.