Passing struct pointers to `Post` method

[dearoneesama]

I noticed that the Post method only supports passing values typed as interface{}, for example, only doing this is valid:

ptr := &struct{}{}
fluent.Post("tag", *ptr)

and passes this check

fluent-logger-golang/fluent/fluent.go

Lines 206 to 209 in 993443f

	msg := reflect.ValueOf(message)
	msgtype := msg.Type()
	if msgtype.Kind() == reflect.Struct {

Passing pointers generates error instead. Can we support passing a struct pointer (use .Elem().Field() to get its fields) and if not, what are possible concerns?

[batara666]

It will panicking on fluentd sys core