JCBC-303:  add 'compile-extern' and 'docszip' to create javadocs
zipfile for deployment to www.couchbase.com

Change-Id: Iebacf85287724a2dbccd407b2f057550de1ceb82
Reviewed-on: http://review.couchbase.org/26614
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>