Polymorphism not used for PrettyWriter

[mondus]

PrettyWritter extends the Writer class but the base class methods are not virtual and as such if a pointer to a PrettyWriter is cast to a Writer the default behaviour is that output is not written using pretty formatting.

See: FLAMEGPU/FLAMEGPU2#1205

[nglass]

I disagree with this approach. Rapidjson is fast because it uses CRTP aka static-polymorphism. Introducing virtual on all the handler callbacks will cause a significant overhead for other users of the library.
IMO you should introduce a writer template to your JSONStateWriter so you can have two implementations. one for writer and one for prettywriter.

It looks like you already do use templates for your JSONGraphWriter

template<typename T> void writeAnyVertex(T &writer