implement streaming requests
require that write() cannot happen after done(), and validate the number of bytes if known
upgrade to node-capnp 0.1.5, improve error handling for streaming requests
Introduce Cap'n Proto interfaces for HTTP APIs.
Merge branch 'streaming' of github.com:dwrensha/sandstorm into inbound-streaming
Clean up inbound streaming. Some issues still present (see TODOs).
Further improve streaming now that we can detect when a capability is remotely closed.
Retry inbound streaming requests on network error (like all other requests).
don't try to compute grainlog data if subscriptions aren't ready
only call shutdownWrite() if there is no expectedSize
Merge pull request #119 from dwrensha/streaming

only call shutdownWrite() when there is no expectedSize
Merge pull request #118 from dwrensha/grain-log-ready

don't try to compute grainlog data if subscriptions aren't ready
make sure not to call openSession more than once
fix typos
Merge pull request #121 from dwrensha/typo

fix typos
Merge pull request #120 from dwrensha/open-session-once

make sure not to call openSession more than once