Instead of producing `{{Module}}.Auto` module, append encoder/decoders inside `{{Module}}` file itself

[choonkeat]

Upside 👍 we don't force the hand of the developers to expose the innards of the types

module Example exposing (Opaque)

type Opaque = Opaque String Int

... more code

-- SPECIAL COMMENT
-- EVERYTHING BELOW IS AUTO GENERATED

autoDecodeOpaque : Json.Decode.Decoder Opaque
autoDecodeOpaque = ... more code

autoEncodeOpaque : Opaque -> Json.Encode.Value
autoEncodeOpaque a = ... more code

Downside 👎 developers will have unignorable diff in their code commits
(instead of inlining, standard encoder decoders should be published as elm package for import to reduce the noise here)