Aiohttp-things

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

* ``AbstractHandler``.

**Changed**

* ``views`` module renamed to ``handlers``;
* classes from ``handlers`` temporarily imported to empty ``views`` module for
backward compatibility.

**Removed**

** ``InstanceMixin`` a synonym for ``ItemMixin``.

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

* Added ``views.PaginationMixin``;
* Added ``ContextMixin``, ``ItemMixin``, ``Jinja2Mixin``, ``JSONMixin``,
``ListMixin``, ``PaginationMixin``, ``PrimaryKeyMixin`` to package namespace.

**Removed**

* ``instance`` attribute removed from ``ItemMixin``, use ``ItemMixin.item``;
* ``pk_factory`` attribute removed from ``PrimaryKeyMixin``, use
``PrimaryKeyMixin.pk_adapter``.

-----------
**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``.