Aiohttp-things

-----------
**Added**
* ``ResponseFormatMixin``

**Changed**
* ``views.InstanceMixin`` class renamed to ``views.ItemMixin``;
* ``views.ItemMixin`` synonym renamed to ``views.InstanceMixin``.

-----------
**Add**

* ``views.PrimaryKeyMixin.pk_adapter`` instead ``views.PrimaryKeyMixin.pk_factory``.

**Deprecated**

* ``views.PrimaryKeyMixin.pk_factory``.

-----------
**Changed**

* ``views.InstanceMixin`` and ``views.ListMixin`` inherited by
``aiohttp.abc.AbstractView``;
* ``views.ItemMixin`` renamed to ``views.InstanceMixin``.

-----------
**Removed**

* ``prepare_context()`` method removed from ``views.ContextMixin`` and
``views.ListMixin``.

-----------
**Added**

** added ``views.Jinja2Mixin`` (need install ``aiohttp-jinja2``);
** added ``views.JSONMxixin``;
** added ``views.ListMixin``;

**Changed**

* ``views.PrimaryKeyMixin`` allocated in a separate mixin;
* ``views.ItemMixin`` inherited by ``views.ContextMixin`` and
``views.PrimaryKeyMixin``.

-------------
**Changed**

* ``views.PrimaryKeyMixin`` renamed to
``views.ItemMixin``.

**Added**

* Added ``views.PrimaryKeyMixin`` synonym for ``views.ItemMixin``.