Utils/Logger: FileTarget implementation

Utils/Logger: Fix routing API ambiguities

Utils/Logger: Completed the target routing and querying API

Utils/Logger: Implement message routing -> logging library is working now
Move 'nil' class into Utils/mpl.hh

Utils/Logger: Documentation
Utils/Logger: Better SENF_LOG_CLASS_AREA integration
Utils/Logger: Fix compile-time config bug for larger configurations

Utils/Logger: New SENF_LOG_CONF syntax supporting not-yet-declared areas and streams
Utils/Logger: Target baseclass

Logger: Implemented compile-time configuration support