Add one more example for custom router macro functions, relative to https://github.com/kataras/iris/issues/918

Former-commit-id: 457c1a94dc8d93e614e9da70e1ec2482fe0c5765

_examples/routing/dynamic-path/main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"regexp"
 	"strconv"
 
 	"github.com/kataras/iris"
@@ -140,6 +141,24 @@ func main() {
 		ctx.Writef("Hello id: %d looking for friend id: ", id, friendid)
 	}) // this will throw e 504 error code instead of 404 if all route's macros not passed.
 
+	// Another example using a custom regexp and any custom logic.
+	latLonExpr := "^-?[0-9]{1,3}(?:\\.[0-9]{1,10})?$"
+	latLonRegex, err := regexp.Compile(latLonExpr)
+	if err != nil {
+		panic(err)
+	}
+
+	app.Macros().String.RegisterFunc("coordinate", func() func(paramName string) (ok bool) {
+		// MatchString is a type of func(string) bool, so we can return that as it's.
+		return latLonRegex.MatchString
+	})
+
+	app.Get("/coordinates/{lat:string coordinate() else 502}/{lon:string coordinate() else 502}", func(ctx iris.Context) {
+		ctx.Writef("Lat: %s | Lon: %s", ctx.Params().Get("lat"), ctx.Params().Get("lon"))
+	})
+
+	//
+
 	// http://localhost:8080/game/a-zA-Z/level/0-9
 	// remember, alphabetical is lowercase or uppercase letters only.
 	app.Get("/game/{name:alphabetical}/level/{level:int}", func(ctx iris.Context) {