This improves compatibility with asyncio test frameworks like
pytest-asyncio.

Fixes #2324

gen: Deprecate legacy interfaces

This temporarily duplicates the tests, but the versions using the
deprecated interfaces will be gone in 6.0

concurrent: Add deprecation warning

auth: Add deprecation warnings for callback-based interfaces

Maintainer dependency updates

flake8 just started complaining about this line for some reason.

Set version to 5.0.1

Update running.rst

minor type

concurrent,httputil,websocket: small bug fixes

Fixes #2280

Fixes #2276

Also accept both bytes and str, and add a client-side ping() method.

Fixes #2295

cherrypick-5.0: asyncio: Support Python 3.4.2 for compatibility with Debian jessie

The ensure_future function was not introduced until 3.4.4, and
some exceptions were changed from AssertionError to RuntimeError in
3.4.3.

Fixes #2301

asyncio: Support Python 3.4.2 for compatibility with Debian jessie

Only invoke select_subprotocol() when the client requests it

The ensure_future function was not introduced until 3.4.4, and
some exceptions were changed from AssertionError to RuntimeError in
3.4.3.

Fixes #2301

Final release notes and version bump for 5.0

docs: Updates for 5.0