Refactor: put public header in another dir

Change-Id: I8e68ce5b663c8c2999b234d1ab47b2507175e150
Reviewed-on: http://review.couchbase.org/32321
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>