Export create_instance on win32

Change-Id: I4894c7c83c09f93cb1d4e7aec60a118ea799ba1d
Reviewed-on: http://review.couchbase.org/31620
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>