Keep order of fields as they are added, not sorting alphabetically

To use json files in a context where human readability makes sense, order of the fields insertion can make sense. As jsoncpp is sorting them alphabetically, it becomes hard to read the file and find related fields in ddifferent ends of the object.
For example
Json::Value root;
root["name"] = "Test;"
root["host"] = "127.0.0.1";
root["port"] = 80;

would be nice to have printed as

{
"name" : "Test,
"host" : "127.0.0.1",
"port" : 80
}

and not as

{
"host" : "127.0.0.1",
"name" : "Test,
"port" : 80
}

I actually succeeded to have this feature by replacing a container used by Json::Value with a custom one.

The issue concerns the container used by Json::Value and the field-order behavior during JSON output. Start by reviewing those existing paths and the insertion-order example. Done means fields are emitted in insertion order rather than alphabetically, with tests covering the reported example and existing behavior.