LevelDebug used for debug messages.

LevelError used for error messages.

LevelFatal used for fatal messages.

LevelInfo used for info messages.

LevelWarning used for warning messages.

Default is the default logger.

Logrus is the default logger, using Sirupsen/logrus as a backend.

Writer accepts messages along with the Level.

WriterC is the context-aware Writer.

Level is the message urgency level.