add csdn auto sync script

+#!/bin/bash
+
+echo "更新CSDN镜像的脚本"
+
+# 创建CSDN镜像的过程如下：
+# 1. 在CSDN上创建项目，从https://github.com/winlinvip/simple-rtmp-server拷贝过来。
+# 2. 在本地虚拟机上：git clone git@code.csdn.net:winlinvip/srs-csdn.git  
+# 3. 创建同步的branch：
+#       git remote add upstream https://github.com/winlinvip/simple-rtmp-server.git
+#       git fetch upstream
+#       git checkout upstream/master -b srs.master
+# 4. 执行本同步更新脚本，更新。
+#       bash scripts/csdn.mirror.sh
+
+echo "argv[0]=$0"
+if [[ ! -f $0 ]]; then 
+    echo "directly execute the scripts on shell.";
+    work_dir=`pwd`
+else 
+    echo "execute scripts in file: $0";
+    work_dir=`dirname $0`; work_dir=`(cd ${work_dir} && pwd)`
+fi
+work_dir=`(cd ${work_dir}/.. && pwd)`
+product_dir=$work_dir
+
+. ${product_dir}/scripts/_log.sh
+ret=$?; if [[ $ret -ne 0 ]]; then exit $ret; fi
+ok_msg "导入脚本成功"
+
+for ((;;)); do
+    git checkout srs.master && git pull
+    ret=$?; if [[ 0 -ne $ret ]]; then 
+        failed_msg "更新github分支失败，自动重试";
+        continue
+    else
+        ok_msg "更新github分支成功"
+    fi
+    break
+done
+
+git checkout master && git merge srs.master
+ret=$?; if [[ 0 -ne $ret ]]; then failed_msg "合并github分支失败, ret=$ret"; exit $ret; fi
+ok_msg "合并github分支成功"
+
+git commit -a -m "merge from github.srs"
+ret=$?; if [[ 0 -ne $ret ]]; then 
+    warn_msg "提交CSDN失败，忽略, ret=$ret";
+else
+    ok_msg "提交CSDN成功"
+fi
+
+for ((;;)); do 
+    git push
+    ret=$?; if [[ 0 -ne $ret ]]; then 
+        failed_msg "提交CSDN分支失败，自动重试";
+        continue
+    else
+        ok_msg "提交CSDN分支成功"
+    fi
+    break
+done
+
+ok_msg "CSDN同步git成功"
+
+exit 0