Slim

* Added: `BaseView.get_x_forwarded_for` method

* Added: `BaseView.get_ip` method

* Changed: Use IOCP eventloop by default on windows system

* Fixed: query operator IS_NOT works

* Added: a new return code named `TOO_FREQUENT`

* Fixed: permission check for records after select remove some columns added by `add_query_condition`.

* Changed: `new` and `set` now accept empty values instead of throw exception.

* Fixed: `SlimExceptions` raised by BaseView.prepare were not caught.

* Fixed: `ErrorCatchContext` didn't catch the ``FinishQuitException`.