docker-compose.override.yml and the docker-compose -f flag

[davidmarkclements]

https://docs.docker.com/compose/extends/#multiple-compose-files

• the docker-compose.override.yml implicitly merges config with the docker-compose.yml file
• when you specify multiple docker-compose files with the -f flag, each subsequent files overrides and merges with the previous

currently config allows specifying multiple docker-compose files, but they aren't merged

if we merge them, the docker-compose.override.yml would just have to specified in the include array

if not, we may need another a merge-include or some such

[davidmarkclements]

merging wont be as simple as converting yaml to object then doing a deep extend, because of polymorphic structures like build (#158)

But.. If, as a rule, all strings that could potentially be objects were converted into object form first then merging would be as simple as deep extend