Change positions of brackets in dump()

[supsm]

There should be an option to change the location of where the brackets go in the dump function.

Currently, all jsons look something like this:

"object": {
    "key": "value"
}

It would be cool if we could have jsons also look like this:

"object":
{
    "key": "value"
}

[nlohmann]

This goes to the long list of detailed feature requests for the dump function. The problem is to find an API that allows to specify call these aspects, yet still remains extendable such that we do not have breaking changes down the road.