Custom JSONDecoder

[florianreinhart]

It should be possible to specific a custom JSONDecoder (ideally per column) for decoding.

In my database there is a JSON column that contains Date values encoded as Unix timestamps.

[tanner0101]

Fixed here: #285, thanks!

Side note, if you're using Fluent, you can use @Timestampwith .unix format instead of needing to configure a custom JSON coder: https://docs.vapor.codes/4.0/fluent/model/#timestamp-format

// Stores date as seconds since UNIX epoch
@Timestamp(key: "updated_at", on: .update, format: .unix)
var updatedAt: Date?