Add func for GetNameForLevel

[codenamoo]

When set customized-output, it may the Name of the level useful rather than
the Text(colorful or not) of the level.

golog.Handle(func(l *golog.Log) bool {
                prefix := golog.GetNameForLevel(l.Level)
                pc, fn, line, _ := runtime.Caller(7)
                message := fmt.Sprintf("%s line %d (%s) (%s) %s: %s",
                        prefix, line, runtime.FuncForPC(pc).Name(), fn, l.FormatTime(), l.Message)

                if l.NewLine {
                        message += "\n"
                }

                fmt.Print(message)
                return true
})

will out like:
warn line 26 (main.main) (/home/pato/go/src/github.com/kataras/golog/_examples/customize-output/main.go) 2018/09/10 09:57: Hey, warning here

Thanks.

[kataras]

Thanks @codenamoo but could you please fix the space in the doc comments of the new function you introduced?

[codenamoo]

Hello @kataras, Thank you for your message. I've fix the indent and run gofmt. Please check again.
(But I worried about github diff shows changed indent for code but not comments.)
Thanks.