v3.1.2

0442912 Fix bug: The length of destination buf be miscalculated.
4370222 Fix bug: Filter '/dev', '/sys' and '/proc' failed when download file.
02d8168 Optimization code.
1e7dc94 Fix bug: URLEncode should be used to encode description, not Base64.
54ddb2f Optimization: Use avl instead of list to manage sessions.
d5ec86c Optimization: reduce the time of memory occupation