optionFormat and eitherFormat should be typed JsonFormat[T]

[fommil]

unfortunately these two implicit methods return very specific types, making them very troublesome to deal with when overriding or doing anything funky with shapless to automatically derive product/trait types.

[fommil]

actually, (performance aside) eitherFormat might be ok. It's just optionFormat that's killing me.

[fommil]

I can workaround this with a non-implicit method of the same name, and introducing an implicit one with the correct return type.

[jkinkead]

This fix broke compatibility with version 1.3.1 - optionFormat has a different return type from 1.3.1, and anything compiled against it will now throw a runtime exception like:

Exception in thread "main" java.lang.NoSuchMethodError: spray.json.DefaultJsonProtocol$.optionFormat(Lspray/json/JsonFormat;)Lspray/json/StandardFormats$OptionFormat;

I'll open a separate issue.

[fommil]

ouch

[fommil]

the workaround is to create an implicit override def that will return the specialised type instead of JsonFormat[Option[T]]