Connection library for mutation streams.

- Includes a server that publishes mutations and error back to application.
- Includes a client that can push mutation to downstream endpoint via one or
  more connections.
- Includes test case and benchmarking.

Change-Id: Ib3b4901f49fcfd1e3434fb5ff5af56f982ae91da
Reviewed-on: http://review.couchbase.org/35433
Reviewed-by: John Liang <johliang00@gmail.com>
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Tested-by: Pratap Chakravarthy <prataprc@couchbase.com>