Add a simple 'Context#GetReferrer', as requested by the People: adapt the goreferrer external package

Former-commit-id: 8f1dce93dd5a2449d806f0b28baf5a8c860193b5

_examples/http_request/extract-referer/main.go

@@ -0,0 +1,29 @@
+package main
+
+import (
+	"github.com/kataras/iris"
+	"github.com/kataras/iris/context"
+)
+
+func main() {
+	app := iris.New()
+
+	app.Get("/", func(ctx context.Context) /* or iris.Context, it's the same for Go 1.9+. */ {
+		// GetReferrer extracts and returns the information from the "Referer" header as specified
+		// in https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Referrer-Policy or by the URL query parameter "referer".
+		r := ctx.GetReferrer()
+		switch r.Type {
+		case context.ReferrerSearch:
+			ctx.Writef("Search %s: %s\n", r.Label, r.Query)
+			ctx.Writef("Google: %s\n", r.GoogleType)
+		case context.ReferrerSocial:
+			ctx.Writef("Social %s\n", r.Label)
+		case context.ReferrerIndirect:
+			ctx.Writef("Indirect: %s\n", r.URL)
+		}
+	})
+
+	// http://localhost:8080?referer=https://twitter.com/Xinterio/status/1023566830974251008
+	// http://localhost:8080?referer=https://www.google.com/search?q=Top+6+golang+web+frameworks&oq=Top+6+golang+web+frameworks
+	app.Run(iris.Addr(":8080"), iris.WithoutServerError(iris.ErrServerClosed), iris.WithoutVersionChecker)
+}