Add whitespaceOptions: colonBraceSameLine to settings

[NotWearingPants]

Fixes #1336 by adding an array option called "whitespaceOptions" to StreamWriterBuilder, and a possible value called "colonBraceSameLine" which causes { and [ following a colon to be placed in the same line.
The option is backed by a flag enum in BuiltStyledStreamWriter.

Example usage:

Json::StreamWriterBuilder builder;
builder.settings_["whitespaceOptions"] = Json::Value { Json::ValueType::arrayValue };
builder.settings_["whitespaceOptions"].append("colonBraceSameLine");

Json::Value json { Json::ValueType::objectValue };
json["hello"] = Json::Value { Json::ValueType::objectValue };
json["hello"]["world"] = "!";
json["world"] = Json::Value { Json::ValueType::arrayValue };
json["world"].append("!");

std::cout << Json::writeString(builder, json) << std::endl;

Result:

{
        "hello": {
                "world": "!"
        },
        "world": [
                "!"
        ]
}

[cdunn2001]

I like this. Thanks. Could use a test though.

Does anyone else have time to review this?

[baylesj]

I'd be happy to review once there is test coverage associated with this.

[NotWearingPants]

Rebased and fixed review comment

[baylesj]

This needs to be formatted and have tests added.

Closing this due to inactivity. Feel free to reopen if you are able to address feedback.