Implement new stream2 API

This embeds the stream_init/1 logic into the stream functions so that we
don't have to maintain the logic for inititalizing the stream for all
clients.

BugzId: 24635
Add margaret counters for stream timeouts

Avoid spamming logs with timeout stacks when there's not a whole lot we
can do with the information.
Merge pull request #21 from cloudant/24635-new-stream-API

Implement new stream2 API