Merge pull request #68 from todesschaf/wip/altsvc

Plumb in ALTSVC
Releasing 2.5.3
Update for new version of http2-protocol
Merge pull request #70 from todesschaf/wip/draft13

Update for new version of http2-protocol
Adding Travis CI support
HTTP tests - fix tests on newer chai versions
README - adding Travis CI badge
HTTP: ignore duplicate writeHead calls after headers are sent. Fixes #71
Make OutgoingResponse listen to the 'CLOSED' state from the underlying stream

We emit 'close' once in this state, and future writes are ignored. AFAICT,
this matches other HTTP behavior in Node.
Respond to connection errors and allow cancellation of responses

If the connection is closed or has an error, send GOAWAY and
close all streams with a RST_STREAM.