adds vendor directory

vendors dependencies in standard `vendor` directory, managed by glide

vendor/github.com/mattn/go-pointer/_example/callback.h

@@ -0,0 +1,9 @@
+#include <unistd.h>
+
+typedef void (*callback)(void*);
+
+static void call_later(int delay, callback cb, void* data) {
+  sleep(delay);
+  cb(data);
+}
+

vendor/github.com/mattn/go-pointer/_example/main.go

@@ -0,0 +1,29 @@
+package main
+
+/*
+#include "callback.h"
+
+void call_later_go_cb(void*);
+*/
+import "C"
+import (
+	"fmt"
+	"unsafe"
+
+	"github.com/mattn/go-pointer"
+)
+
+type Foo struct {
+	v int
+}
+
+func main() {
+	f := &Foo{123}
+	C.call_later(3, C.callback(C.call_later_go_cb), pointer.Save(f))
+}
+
+//export call_later_go_cb
+func call_later_go_cb(data unsafe.Pointer) {
+	f := pointer.Restore(data).(*Foo)
+	fmt.Println(f.v)
+}