performance: Refactor how data is managed to reduce copying. * Make use of `collections.abc.Mapping` to better identify things that are supposed to look like dictionaries. * Instead of handling "overlay" of data in a dict tree in each different data object, make all objects `Mapping`s and handle merging at a higher level with the new `MergedMapping` object. * Since this new object is read-only, remove the need for deep-copying of app and page configurations. * Split data classes into separate modules.

from piecrust.serving.server import Server


def get_app(root_dir, sub_cache_dir='prod', enable_debug_info=False):
    server = Server(root_dir,
                    sub_cache_dir=sub_cache_dir,
                    enable_debug_info=enable_debug_info)
    app = server.getWsgiApp()
    return app