Rororo

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- Add ``rororo.aio`` module with:

- ``add_resource_context`` context manager
- ``is_xhr_request``, ``parse_aioredis_url`` utility functions

- Update flake8 config & bump aiohttp version for tests
- Added ChangeLog & modified GitHub Releases Page

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- Adds ability to supply custom error class while making manual errors by
``schema.make_error`` method
- Default validator class preset default values from schema to instance for
validation
- Several improvements to test process

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- New beginning for rororo project. Now it is a bunch of helper methods instead
of yet another web-framework.