Documentation still references automatic record constructor

[Jwashton]

A number of the examples in the documentation are now misleading after automatic record constructors were removed from the language in gren-lang/compiler#41.

For example, this code in the documentation for Json.Decode.map2

type alias Point =
    { x : Float, y : Float }

point : Decoder Point
point =
    map2 Point -- Compiler error: I cannot find a `Point` variant
        (field "x" float)
        (field "y" float)

Here's a list of the places I've found where this occurs:

• Dict.Dict
• Bytes.Decode.map2
• Bytes.Encode.encode (in a comment at the end)
• Json.Decode.dict (twice)
• Json.Decode.map2
• Json.Decode.map3
• Json.Decode.lazy