add ota algorithm for device

1. effective "Differential Upgrade" patch algorithm with high compression rate
2. effective recovery algorithm support recovery firmware in blocks which has low memory consumption and wear-leveling strategies, especially suitable for embeded devices with low RAM.
3. add sample ota bootloader project, see:
board\TencentOS_tiny_EVB_MX_Plus\KEIL\ota\ota_bootloader_recovery
4. add sample application project for download firmware through http, see:
board\TencentOS_tiny_EVB_MX_Plus\KEIL\ota\ota_application_download_through_http
5. add sample application project for download firmware through qcloud explorer console, see:
board\TencentOS_tiny_EVB_MX_Plus\KEIL\ota\ota_application_download_through_qcloud_iot_explorer
6. an OTA markdown document is pending

components/ota/common/diff/segment_tree.h

@@ -0,0 +1,50 @@
+/*----------------------------------------------------------------------------
+ * Tencent is pleased to support the open source community by making TencentOS
+ * available.
+ *
+ * Copyright (C) 2019 THL A29 Limited, a Tencent company. All rights reserved.
+ * If you have downloaded a copy of the TencentOS binary from Tencent, please
+ * note that the TencentOS binary is licensed under the BSD 3-Clause License.
+ *
+ * If you have downloaded a copy of the TencentOS source code from Tencent,
+ * please note that TencentOS source code is licensed under the BSD 3-Clause
+ * License, except for the third-party components listed below which are
+ * subject to different license terms. Your integration of TencentOS into your
+ * own projects may require compliance with the BSD 3-Clause License, as well
+ * as the other licenses applicable to the third-party components included
+ * within TencentOS.
+ *---------------------------------------------------------------------------*/
+
+#ifndef _SEGMENT_TREE_H_
+#define  _SEGMENT_TREE_H_
+
+typedef struct segment_tree_node_st {
+    int     left;
+    int     right;
+    int     mid;
+    int     is_covered;
+} stree_node_t;
+
+typedef struct segment_tree_st {
+    stree_node_t   *nodes;
+    int             length;
+    int             left;
+    int             right;
+} stree_t;
+
+int segtree_create(stree_t *stree, int left, int right);
+
+int segtree_destroy(stree_t *stree);
+
+int segtree_reset(stree_t *stree);
+
+int segtree_insert(stree_t *stree, int left, int right);
+
+int segtree_delete(stree_t *stree, int left, int right);
+
+int segtree_query(stree_t *stree, int left, int right);
+
+int segtree_cal(stree_t *stree);
+
+#endif
+