Bulb-channels

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* Fix unicode issues with test client under Python 2.7

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* Class-based consumer pattern and WebSocket consumer now come with Channels
(see docs for more details)

* Better testing utilities including a higher-level Client abstraction with
optional HTTP/WebSocket HttpClient variant.

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* enforce_ordering now queues future messages in a channel rather than
spinlocking worker processes to achieve delays.

* ConsumeLater no longer duplicates messages when they're requeued below the
limit.

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* Backpressure is now implemented, meaning responses will pause sending if
the client does not read them fast enough.

* DatabaseChannelLayer has been removed; it was not sensible.

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* HTTP paths and query strings are now expected to be sent over ASGI as
unescaped unicode. Daphne 0.11.0 is updated to send things in this format.

* request.FILES reading bug fixed

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* ChannelTestCase base testing class for easier testing of consumers

* Routing rewrite to improve speed with nested includes and remove need for ^ operator

* Timeouts reading very slow request bodies