[Feature Request] Allow distinguishing between lists and objects

[alecb-stripe]

It might be nice to support flattened paths that distinguish between list indexes and object keys.

E.g., this:

{
  "foo": {
    "0": ["bar", {"baz": "bam"}],
  }
}

might be flattened to:

{
  "foo.0[0]": "bar",
  "foo.0[1].baz": "bam",
}