Add nested field access

[sagg0t]

Currently only top level fields can be accessed to configure their output format.
Arrays/maps are printed as prettified JSON.

Need to be able to access lower lever objects so only specific nested attributed is printed instead of the whole structure.

Config might look like

- name: duration
  path:
  - a
  - b
  - c

and an entry for the given config would be something like

{
    "a": {
        "b": {
            "c": { "duration": 123 }
        }
    }
}