add documentation for pub/sub options
add documentation for pub/sub options

crossbario/autobahn-js,oberstet/autobahn-js,tavendo/AutobahnJS,crossbario/autobahn-js,tavendo/AutobahnJS,tavendo/AutobahnJS,oberstet/autobahn-js,oberstet/autobahn-js,crossbario/autobahn-js,oberstet/autobahn-js,crossbario/autobahn-js