CHORE: Refactored Yell::Formatter#format => #call
FIX: initializing HashWithIndifferentAccess directly within config
ST: Make Yell better backwards compatible the the standard Ruby logger
ST: Implemented backwards compatible :add method to logger (sacrifices some functionality)
ST: Updated Yell::Logger#name to always return a value (though not always add to the Yell::Repository)
ST: Further refactorings for backwards compatibility
ST: Updated the silencer API
ST: Preserving API for external yell adapters and legacy Logger backwards compatibility