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/lzma/3rdparty/Sha256.h

@@ -0,0 +1,26 @@
+/* Sha256.h -- SHA-256 Hash
+2013-01-18 : Igor Pavlov : Public domain */
+
+#ifndef __CRYPTO_SHA256_H
+#define __CRYPTO_SHA256_H
+
+#include "7zTypes.h"
+
+EXTERN_C_BEGIN
+
+#define SHA256_DIGEST_SIZE 32
+
+typedef struct
+{
+  UInt32 state[8];
+  UInt64 count;
+  Byte buffer[64];
+} CSha256;
+
+void Sha256_Init(CSha256 *p);
+void Sha256_Update(CSha256 *p, const Byte *data, size_t size);
+void Sha256_Final(CSha256 *p, Byte *digest);
+
+EXTERN_C_END
+
+#endif