Add Go codes to docs, including

the chapter of stack and queue, the chapter of tree.

codes/go/chapter_tree/binary_tree_dfs_test.go

@@ -5,6 +5,7 @@
 package chapter_tree
 
 import (
+	"fmt"
 	"testing"
 
 	. "github.com/krahets/hello-algo/pkg"
@@ -14,18 +15,21 @@ func TestPreInPostOrderTraversal(t *testing.T) {
 	/* 初始化二叉树 */
 	// 这里借助了一个从数组直接生成二叉树的函数
 	root := ArrayToTree([]int{1, 2, 3, 4, 5, 6, 7})
-	t.Log("初始化二叉树: ")
+	fmt.Println("初始化二叉树: ")
 	PrintTree(root)
 
 	// 前序遍历
-	nums := preOrder(root)
-	t.Log("前序遍历的结点打印序列 =", nums)
+	nums = nil
+	preOrder(root)
+	fmt.Println("前序遍历的结点打印序列 =", nums)
 
 	// 中序遍历
-	nums = inOrder(root)
-	t.Log("中序遍历的结点打印序列 =", nums)
+	nums = nil
+	inOrder(root)
+	fmt.Println("中序遍历的结点打印序列 =", nums)
 
 	// 后序遍历
-	nums = postOrder(root)
-	t.Log("后序遍历的结点打印序列 =", nums)
+	nums = nil
+	postOrder(root)
+	fmt.Println("后序遍历的结点打印序列 =", nums)
 }