Config docs needing cleanup

/**

• • set($key, $val) will override any previously set $key
• • default($key, $val) will never override set() or previous default() calls
• • get($key) will throw an exception if the $key has not been set
• @export(Usage.Config.notes)
  */

Todos

These were supposed to be TODOs... but I think they're better as guidance for writing comprehensive docs.
/**

• • config file loading... set() should generally be able to override configs from the file
• • Do config file contents automatically get loaded into Liaison? Maybe, if they're namespaced, at least?
• • Should I limit access to set() & get(). NOT EARLY ON

• - maybe in the future? I'm concerned about performance, the time to implement, and how much it's actually needed (assuming you only run code you trust)  
  

• • What happens if a config value is overridden? Error? Let it happen? Fail silently? Log?
• • add conflict resolution for duplicate config keys
• • consider a non-exception approach to a not-set config key
• @export(TODO.Config)
  */