Documentation additions

- Provide note about timeout settings accuracies
- Include recently added operations for lcb_cntl
- Add documentation about error classifiers

Change-Id: Iac820318749f88968ac657a68186793d00863018
Reviewed-on: http://review.couchbase.org/35002
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>