CheckLevel checks whether the log level is valid.

Debug logs a message with severity DEBUG.

Error logs a message with severity ERROR.

Fatal logs a message with severity ERROR followed by a call to os.Exit().

GetLevel get the log level string.

Info logs a message with severity INFO.

SetLevel sets the log level.

SetOutput set the destination for the log output.

Warn logs a message with severity WARN.

LogFormatter is used to format log entry.