Some tweaks for reading/writing

[helly25]

Some tweaks:

• Make json.h an IWYU import header.
• Change Reader::parse to take its document parameter as std::string_view.
• Add static void StreamWriterBuilder::updateDefaults(const Json::Value& settings);
  • Allows to set the global configuration.

[helly25]

@baylesj could you review this?

[baylesj]

@baylesj could you review this?

Thanks for this patch. I have (obviously) not been super active in this repository as of late but am intending to provide a little bit more active stewardship. I am happy to review.