Release: SEnginx v1.5.7

Changes:

    *) Feature: add session base persistence method.

    *) Feature: upgrade naxsi to version 0.5.3.

    *) Change: Delete "robot_mitigation_whitelist_any" directive.

    *) Bugfix: fix the bug in IP whitelist.

    *) Bugfix: fix the compilation problem of naxsi in 32-bit CentOS 6 environment.

    *) Bugfix: add "path" option to the cookie generated by "insert cookie persistence".

Signed-off-by: paulyang <y_y@neusoft.com>