log package implements a simple log service.
1、func New(out io.Writer, prefix string, flag int) *Logger
New to create a Logger.
Parameter setting out the log information is written to the destination.
Parameters prefix is added to the front of each log produced.
Parameters flag custom log attributes (time, files, etc.).
2、Print
（1）func Print(v ...interface{})
Output generated call Print formatted string to the standard output logger, the same methods and parameters fmt.Print process.
（2）func Printf(format string, v ...interface{})
Output generated call Printf formatted string to the standard output logger, the same methods and parameters fmt.Printf process.
（3）func Println(v ...interface{})
Output generated call Println formatted string to the standard output logger, the same methods and parameters fmt.Println process.
3、Fatal
（1）func Fatal(v ...interface{})
Fatal equivalent to {Print (v ...); os.Exit (1)}
（2）func Fatalf(format string, v ...interface{})
Fatalf equivalent to {Printf (v ...); os.Exit (1)}
（3）func Fatalln(v ...interface{})
Fatalln equivalent to {Println (v ...); os.Exit (1)}
4、Panic
（1）func Panic(v ...interface{})
Panic equivalent to {Print (v ...); panic (...)}
（2）func Panicf(format string, v ...interface{})
Panicf equivalent to {Printf (v ...); panic (...)}
（3）func Panicln(v ...interface{})
Panicln equivalent to {Println (v ...); panic (...)}