support feature like Interp.RunFunc("fmt.Println")

[lx217197]

Now:
mContext := igop.NewContext(0)
pkg, err := mContext.LoadDir("./go/item", false)
if err != nil {
panic(err)
}
mInterp, _ := mContext.NewInterp(pkg)
r, err := mInterp.RunFunc("NewStructure", nil)
if err != nil {
panic(err)
}

---

---

Want:
mContext := igop.NewContext(0)
pkg, err := mContext.LoadDir("./go", false)
if err != nil {
panic(err)
}
mInterp, _ := mContext.NewInterp(pkg)
r, err := mInterp.RunFunc("item.NewStructure", nil)
if err != nil {
panic(err)
}