accesslog: add CSV format

relative to: https://github.com/kataras/iris/issues/1601

_examples/logging/request-logger/accesslog-csv/access_log.csv.sample

@@ -0,0 +1,5 @@
+Timestamp,Latency,Code,Method,Path,IP,Req Values,In,Out,Request,Response
+1599900695933,0s,200,GET,/,::1,sleep=35ms,575,81,,Index
+1599900696207,0s,404,GET,/notfound,::1,,572,92,,Not Found
+1599900696693,0s,200,GET,/,::1,,564,81,,Index
+1599900697988,1s,200,GET,/,::1,sleep=1s,573,81,,Index

_examples/logging/request-logger/accesslog-csv/main.go

@@ -0,0 +1,34 @@
+package main
+
+import (
+	"time"
+
+	"github.com/kataras/iris/v12"
+	"github.com/kataras/iris/v12/middleware/accesslog"
+)
+
+func main() {
+	app := iris.New()
+	ac := accesslog.File("access_log.csv")
+	ac.SetFormatter(&accesslog.CSV{
+		AutoFlush: true,
+		Header:    true,
+		// DateScript:   "FROM_UNIX",
+		LatencyRound: time.Second,
+	})
+
+	app.UseRouter(ac.Handler)
+	app.Get("/", index)
+
+	app.Listen(":8080")
+}
+
+func index(ctx iris.Context) {
+	if sleepDur := ctx.URLParam("sleep"); sleepDur != "" {
+		if d, err := time.ParseDuration(sleepDur); err == nil {
+			time.Sleep(d)
+		}
+	}
+
+	ctx.WriteString("Index")
+}