Proguard needs to be notified to keep the twowayview classes.

Hi, 
I've used the previous twoway-view standalone adapterview implementation in a few projects and it saved me a LOT of time.  Thanks for an awesome library!  :+1: 
Now I'm starting to port things to the new one, but I had an annoying non-descript crash while trying to instantiate the LayoutManager. 

After a day of hair pulling it turns out its a silly noob issue with ProGuard deleting the twoway-view classes since I forgot to add a -keep line to the proguard-rules.

Would be great if you accept the pull request or add it to the Readme, it might save someone a lot of time :)


Keep up the good work, 

Blaz