Support other datatypes such as Dates / Disallow other datatypes

[JeremyMoeglich]

Currently datatypes such as Dates, Sets or Maps are not supported as JSON can't represent those types.

The solutions I'm thinking of are:

1. Only allow types that can be converted losslessly to JSON, for example JsonValue in the library type-fest
2. Don't use JSON and use an alternative, libraries such as devalue and serialize-javascript might be an option

[philcockfield]

https://github.com/Rich-Harris/devalue