add explanation why the 'globalVisitorsController' example is a Singleton, because it was not clear for new gophers previously.

Former-commit-id: 9267c415e53eeb00adadf6fde9e0aeeb415cf24a

_examples/mvc/singleton/main.go

@@ -10,7 +10,7 @@ import (
 
 func main() {
 	app := iris.New()
-	mvc.New(app.Party("/")).Register(new(globalVisitorsController))
+	mvc.New(app.Party("/")).Register(&globalVisitorsController{visits: 0})
 
 	// http://localhost:8080
 	app.Run(iris.Addr(":8080"))
@@ -18,10 +18,13 @@ func main() {
 
 type globalVisitorsController struct {
 	// When a singleton controller is used then concurent safe access is up to the developers, because
-	// all clients share the same controller instance instead. Note that any controller's methods
-	// are per-client, but the struct's field can be shared accross multiple clients if the structure
-	// does not have any dynamic struct field depenendies that depend on the iris.Context,
-	// this declares a Singleton, note that you don't have to write a single line of code to do this, Iris is smart enough.
+	// all clients share the same controller instance instead.
+	// Note that any controller's methods
+	// are per-client, but the struct's field can be shared across multiple clients if the structure
+	// does not have any dynamic struct field depenendies that depend on the iris.Context
+	// and ALL field's values are NOT zero, at this case we use uint64 which it's no zero (even if we didn't set it
+	// manually ease-of-understand reasons) because it's a value of &{0}.
+	// All the above declares a Singleton, note that you don't have to write a single line of code to do this, Iris is smart enough.
 	//
 	// see `Get`.
 	visits uint64

mvc/di/reflect.go

@@ -4,8 +4,11 @@ import "reflect"
 
 var emptyIn = []reflect.Value{}
 
-// IsZero returns true if a value is nil, remember boolean's false is zero.
+// IsZero returns true if a value is nil.
 // Remember; fields to be checked should be exported otherwise it returns false.
+// Notes for users:
+// Boolean's zero value is false, even if not set-ed.
+// UintXX are not zero on 0 because they are pointers to.
 func IsZero(v reflect.Value) bool {
 	switch v.Kind() {
 	case reflect.Struct: