Support for docker compose version 3

[rdlf0]

When trying to use a docker-compose.yml file with version 3 syntax, I get the following error:

ERRO[0000] Could not parse config for project myprojectname : yaml: unmarshal errors:
  line 1: cannot unmarshal !!str `3` into config.RawService

Rolling back to version 2 solves the problem, but there are features from version 3 which I need.

[enavarro222]

One can see issue : #421

[CpuID]

The first half of this is covered by #507 (actually parsing the version string in the file). The v3 specific file features may still be missing and need work though, TBD.