add access to lcb timings, including ability to enable and disable

Underlying libcouchbase has a feature that allows users to enable timings on operations and gather timings information as seen at a probepoint in libcouchbase. This enhancement request is to allow for enabling these timings and getting information back.

As had been discussed earlier, this won't help a user understand the actual overall operation times since there could be significant time going into parsing large documents, etc. Still, the idea here is to be able to have a simple probe point at the client side and at the server side (which exists already with "cbstats timings") to determine where to look next. By giving the user programmatic access to the already existing libcouchbase timings, we'd achieve that goal.