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

travis.yml: Fix build on nightly python

docs: Add warnings about DNS rebinding attacks

Fixes #2256

docs: Small updates

Fixes #2279

Fixes #2283

docs: Updates for sphinx 1.7

This introduced a new inherit-docstring option that we don't want
(it currently breaks our docs build) and got stricter about `:arg`
types.

curl_httpclient: Only call native_str on debug message when needed

Some debug messages are binary blobs that should not be decoded.

Fixes #2275

Fix/etag304

Fix typo in URLSpec.__init__ docstring

StaticFileHandler would return a 304 despite the client sending
a non-matching Etag header when If-Modified-Since matches