missing chapter on implementing interfaces?

[aaylward]

Thanks for making this neat guide!

Just a heads up, I get a 404 visiting https://github.com/forax/java-guide/blob/master/guide/chapter19-implementing_interface.md

[forax]

I'm still struggling with this chapter in my head, and sadly, i've not a lot of slack time ... I hope to be able to comeback to work on that guide during christmas