Handle invalid authorities better

[Lukasa]

Found when fuzzing hyper-h2 with afl:

Traceback (most recent call last):
  File "script.py", line 10, in <module>
    c.receive_data(sys.stdin.read())
  File "/Users/cory/tmp/fuzz-results/env/lib/python2.7/site-packages/h2/connection.py", line 891, in receive_data
    for frame in self.incoming_buffer:
  File "/Users/cory/tmp/fuzz-results/env/lib/python2.7/site-packages/h2/frame_buffer.py", line 159, in next
    f.parse_body(memoryview(self.data[9:9+length]))
  File "/Users/cory/tmp/fuzz-results/env/lib/python2.7/site-packages/hyperframe/frame.py", line 706, in parse_body
    self.parse_origin(data[pos:])
  File "/Users/cory/tmp/fuzz-results/env/lib/python2.7/site-packages/hyperframe/frame.py", line 682, in parse_origin
    scheme, hostport = data.split(b'://')
ValueError: need more than 1 value to unpack

We should aim to raise a hyperframe-specific exception here, not just a ValueError. We then need to catch it in hyper-h2.