[WIP] SPDY transport

This pull request implements a transport session by using 'libchan-ref' for nested channels.

* [x] one directional channels
* [x] embed channels from the client to the server
* [x] embed channels from the server to the client
* [ ] embed byte streams
* [ ] go through all the FIXME and check if I'm mad

Like I said, it's a WIP!