View#fetch_all - async method for fetching all records

Change-Id: Id42af81ca4e2748e3fe7588c2a87bbf8d1aea76f
Reviewed-on: http://review.couchbase.org/24027
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>