py-h11: updated to 0.8.0

v0.8.0:

Backwards incompatible changes:
h11 now performs stricter validation on outgoing header names and header values: illegal characters are now rejected (example: you can't put a newline into an HTTP header), and header values with leading/trailing whitespace are also rejected (previously h11 would silently discard the whitespace). All these checks were already performed on incoming headers; this just extends that to outgoing headers.
New features:
New method :meth:Connection.send_failed, to notify a :class:Connection object when data returned from :meth:Connection.send was not sent.

Bug fixes:
Make sure that when computing the framing headers for HEAD responses, we produce the same results as we would for the corresponding GET.
Error out if a request has multiple Host: headers.
Send the Host: header first, as recommended by RFC 7230.
The Expect: header is case-insensitive, so use case-insensitive matching when looking for 100-continue.

Other changes:
Better error messages in several cases.
Provide correct error_status_hint in exception raised when encountering an invalid Transfer-Encoding header.
For better compatibility with broken servers, h11 now tolerates responses where the reason phrase is missing (not just empty).
Various optimizations and documentation improvements.

(adam)