Aiohttp-healthcheck

- Fix for 'Inappropriate ioctl for device' error on posix systems.

- Adds support for init_app construction of healthcheck objects. Thanks to
Iuri de Silvio for the pull request.

- Adds support for Python 3.x. Thanks to Guilherme D'Amoreira for the pull
request.

- Added the `EnvironmentDump` class which provides a second endpoint for
details about your application's environment.

- Incremented the version number to indicate that this is a stable release.

- Added caching to health check responses. Successful checks are cached for 27
seconds; failures are cached for 9 seconds.
- Removed the "simple" view of the health check, which had been available with
the query string `?simple=true`. This isn't necessary now that we cache the
results of the checks.
- Added `timestamp` field to the outer level of the JSON response, and
`timestamp` and `expires` to each check result.