Duplicate field names in the Json have incorrect comments, and nested classes from Config cannot be outside the Config class

[spoorn]

Was trying to use OmegaConfig instead of Cloth Config for my mod (https://www.curseforge.com/minecraft/mc-mods/spoorn-bounty-mobs), due to issues with Lists and Maps always reverting to default values: https://github.com/shedaniel/cloth-config/issues/104.

Noticed that nested config classes are only supported if they are inner static classes of the root Config class which would be annoying refactoring for me.

Also noticed that duplicate field names in the Json would cause incorrect comments because the OmegaConfig logic does not take into account that scenario and just overrides with the last comment for a field name

I already submitted a PR to fix this: https://github.com/Draylar/omega-config/pull/21, but putting up an Issue so it's more easily searchable in case others run into the same problem