修改FETCH API函数名为tango_cache_fetch_object；增加DELETE API；调整ctx结构体内部结构；

cache/tango_cache_xml.cpp

@@ -58,7 +58,7 @@ int construct_complete_xml(struct tango_cache_ctx *ctx, char **xml, int *len)
 	xmlNewProp(root, (const xmlChar *)"xmlns",(const xmlChar *)"http://s3.amazonaws.com/doc/2006-03-01/");
 	xmlDocSetRootElement(pdoc, root);
 
-	TAILQ_FOREACH(etag, &ctx->cache_head, node)
+	TAILQ_FOREACH(etag, &ctx->put.etag_head, node)
 	{
 		sprintf(number, "%u", etag->part_number);
 		child = xmlNewChild(root, NULL, (const xmlChar*)"Part", NULL);