generic logger interface

logger.go

// Log is a package level variable, every program should access logging function through "Log"
var Log Logger

// Logger represent common interface for logging function
type Logger interface {
	Errorf(format string, args ...interface{})
	Fatalf(format string, args ...interface{})
	Fatal(args ...interface{})
	Infof(format string, args ...interface{})
	Info( args ...interface{})
	Warnf(format string, args ...interface{})
	Debugf(format string, args ...interface{})
	Debug(args ...interface{})
}