[feature] extend string interpolation syntax to add 'json' interpolator

[jiahut]

It's an easy-to-use library with handing json. I just do my best to add a feature to make It better.

[wspringer]

Thanks jiahut! I have been considering if I wanted to support this type of String interpolation, but I'm not entirely convinced just yet. First of all, I think you will find that for almost all cases, the builders actually offer a way more compact notation, with less boilerplate.

Perhaps if there is a list of examples where this clearly shows a benefit over the builders, I might be willing to pull it in. It's a cool feature, but adding cool features is not an objective. It needs to be useful as well. And I'd argue completeness is not achieved if there's no longer anything to add, but if there's no longer anything left to remove. ;-)