Update to 3.0.5 api, intermediate work

I'm trying to get this plugin to work with the new PouchDB 3.0.5. 
Half success is accomplished, two browser can talk over the data channel to each other, but the exchanged `rpcAPI` object does not work for me. I get a `this._bulkDocs(...) is undefined` error when writing anything to the remote DB. My guess is there are changes to `AbstractPouchDB` on how custom adapters are registered, but from reading the source I could not figure this out. Your entry https://github.com/pouchdb/pouchdb/wiki/Writing-custom-adapters is the only thing I can find.

It would be cool to get this to work. More browsers are supporting webRTC, so it will become a real communication channel. My wish is syncing a mobile Chrome to a desktop Chrome, without having an intermediate server located database.