Best practises for developing add-ons

[lcmen]

Hello @fgrehm,
I love the idea of the project. I've been searching for an easy way to isolate my dev environment without tinkering with VM s or Dockerfiles and the project seems very good candidate :).

I have a few questions though:

1. I would like to create add-on for ElasticSearch, where should I start? How your workflow for developing add-ons looks like?
2. I would like to use Postgres 9.5. is there an easy way to use different versions?