aiohttp 0.16.5 bugfix release

The release finally fixes all issues in multidicts related to Cython but for removing current exception if present.

The fixed bug is important enough: it may lead to Python interpreter crash with segfault in some cases.
aiohttp development team strongly recommends upgrading to new version.

See #410 for details.

Changes

• Get rid of all comprehensions and yielding in _multidict #410