adds vendor directory

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

vendor/github.com/mattn/go-gtk/example/clipboard/clipboard.go

@@ -0,0 +1,19 @@
+package main
+
+import (
+	"fmt"
+	"github.com/mattn/go-gtk/gdk"
+	"github.com/mattn/go-gtk/gtk"
+)
+
+func main() {
+	gtk.Init(nil)
+	clipboard := gtk.NewClipboardGetForDisplay(
+		gdk.DisplayGetDefault(),
+		gdk.SELECTION_CLIPBOARD)
+	fmt.Println(clipboard.WaitForText())
+	clipboard.SetText("helloworld")
+	gtk.MainIterationDo(true)
+	clipboard.Store()
+	gtk.MainIterationDo(true)
+}