INI: remove need for [filters] section and perform all object configuration in [main]

The [main] section and the [filters] section are really just a pool of objects, keyed by name, but the pools can't 'share' objects from one another. So if you configured something in [main] that needed to be referenced from a custom filter in [filters], that is not possible at the moment. By putting everything in the main 'pool', objects can reference each other as needed.