Add cJSON from libvbucket

Change-Id: I86813432919dbb8bbc42ee4efdc86393039b0806
Reviewed-on: http://review.couchbase.org/34637
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>