Asgish

* Fix lifespan messages (cleanup -> shutdown)

* Introduce testing utilities: classes that run servers when used as a context manager. One using subprocesses, one using a mock ASGI server.
* The above allows us to properly measure our test coverage.
* The test coverage is raised to 100% for all relevant modules.
* Raise` EOFError` instead of `IOError` upon connection/ws close.
* Add invoke `tasks.py` for easier dev.
* Doc tweaks.

* Update docs and metadata to mark Asgish as Beta.

* Support for ASGI lifetime messages.
* Improvements to logging (e.g. `exc_info` in included).

* More tests.
* Improvements to websockets implementation.
* Refactoring.
* Responses are more strict (2-element tuple must be (dict, body)).
* Rename `handler2asgi` to `to_asgi`.

First sorta official release.