Add default advertised host and topic creation

[cyx]

Reasons for change

• Need the ability to link things together in docker-compose, and having a default good ADVERTISED_HOST seemed like a good default.
• Create topics becomes laborious if done imperatively, so having it declarative in a docker-compose.yml enviroment section seems a tad better.

TODO

• README updates

[rawkode]

Thanks for this patch, @cyx - I was looking for exactly this.

I've forked this Dockerfile and pulled your patch and published to the Docker Hub

All commits still in-tact, and hopefully @mbruggmann notices that a lot of people use this library and picks up the maintenance

https://hub.docker.com/r/rawkode/kafka/

[mbruggmann]

Maybe @dflemstr knows more about the newer kafka versions? I haven't had time to keep up with recent developments unfortunately...

[rawkode]

@mbruggmann there are 23 pull requests, most without dialog. May I suggest that you add something to the README that says pull requests won't be accepted and that this image is unlikely to change? (If that is the case, of course)