Also:
- randomized tests
- fixed dependent tests
- updated ci requirements
- added tox.ini

Update README.md

Reflecting newer versions of aiohttp API

The copying_task_factory does not share the context
when creating new tasks and uses a copy of it.
This is to allow created tasks to modify their context
without mirroring the change into every other task, but
whilst still passing along a copy of their own context
to their children.

Prepare for release

Before every asyncio method had to be rewritten to
propagate the context. Now the task factory is
the one in charge of doing that

- Added README
- Added basic context api with set and get methods
- Tests for set and get methods
- Integration with Travis
- Integration with Coveralls