Feature: merge multiple config paths

[circulon]

This PR provides the ability to "stack" config as a hierarchy.

The reason being that not all environments should contain every customisation in environmet vars.
This provides the ability to override specific keys in dicts and append items to lists in the config in a very simple and obvious way.

example loader:

self.application.bind("config.location", "config.base")
configuration = Configuration(self.application)
configuration.load([
    "config.environment.prod",
    "config/deployed",
])  

this will load and update the config in the following order from lowest to highest priority:

• config.base
• config.environment.prod
• config.deployed